One Shoreline

Errata note (26 Oct 2026): this is the v1.3 essay, the edition of record. Its front matter still says "v1.2" and "21 October 2026"; see OS-E02. The text below is unchanged.

The postcard

In 1898 a camera crew from Thomas Edison's company came to Coronado. Among the short films they made was Off for the Rabbit Chase, shot at the Hotel del Coronado. The San Diego History Center's filmography of the region opens with that year's three Edison titles, which makes them among the first motion pictures made in San Diego [1][2].

Billy Wilder filmed Some Like It Hot at the Del in 1958, its turrets standing in for a Florida resort. Richard Rush shot The Stunt Man there in 1977 and 1978, with a scene at La Jolla's Children's Pool. The hotel was named a National Historic Landmark in 1977 [2][3]. In 2012 Stephen Leatherman, the coastal scientist known as Dr. Beach, ranked the beach in front of it the best in America [4].

The bay behind the hotel has its own record. Glenn Curtiss ran a flying school on North Island from 1911. The air station was commissioned in 1917. On 10 May 1927 Charles Lindbergh took off from North Island on the first leg of the journey that ended in Paris. By 1935 four aircraft carriers were based there, and during the Second World War dredging filled the Spanish Bight, the channel that had made Coronado two islands [5][6]. Across the water the Star of India, launched in 1863 and the oldest ship still sailing regularly, is moored at the Embarcadero [7]. In the 1940s an estimated 95 percent of the tuna canned in the United States was canned here [8].

That history is part of why people came, and kept coming. The climate, the harbour, the military and the border economy built a region that now holds more than six and a half million people on the two sides of the line (Figure 3) [9][10].

Growth has a cost

Both sides grew for many of the same reasons. Mexico's border industrialization program began in the mid-1960s, and the assembly plants it brought, the maquiladoras, tied Tijuana's economy to California's [11]. On 30 November 1965 the two countries' boundary and water commission signed Minute 222, an emergency connection of Tijuana's sewage to San Diego's metropolitan system [12]. The region shared a pipe a generation before it shared a trade agreement.

The pipes did not keep pace. Tijuana's collection system was designed for about 600,000 people [13]. The municipality counted 461,267 in 1980 and 1,922,523 in 2020, more than three times the design population (Figure 1) [9][14]. On the U.S. side, the South Bay International Wastewater Treatment Plant, built with $239.4 million from Congress, opened in 1997 at 25 million gallons a day, treating sewage only to an advanced-primary level. A federal court set 30 September 2008 as the deadline for it to meet the Clean Water Act; it missed it [15]. Secondary treatment came online in late 2010, and the plant met its permit consistently only from 2013 [16]. It reached 35 million gallons a day in August 2025, and a 50-million-gallon design is scheduled [17]. In December 2025 the two governments signed Minute 333, a new calendar of works on both sides [18].

The hidden side: water

None of this is hidden. It is simply hard to see. On a satellite image the coast looks continuous, one long beach from Coronado past the border to Punta Bandera (Map 1). The water arriving on it comes from several places.

The Tijuana River drains a watershed that lies mostly in Mexico and reaches the sea through an estuary just north of the border. About ten kilometres south of the border, sewage that the San Antonio de los Buenos plant cannot treat runs onto the beach at Punta Bandera [20]. Scripps researchers who modelled every transboundary flow in 2017 found that in wet weather the river caused about two-thirds of the closures; overall, the dominant source was the Punta Bandera discharge, and in the dry season it accounted for every closure at the Imperial Beach pier [19]. Under the south swells of summer, waves carry that water north through the surf zone, and DNA tracing has followed it as far as Silver Strand State Beach, about 20 kilometres away [20].

Mexico rebuilt the San Antonio de los Buenos plant in 2025 to treat 800 litres a second; Rosario Norzagaray of the group Costa Salvaje says its late-1980s design was 1,200, for a city of about 900,000 [21]. In September 2025 the head of Tijuana's water utility, CESPT, told a state legislative committee that only 6 of the city's 16 treatment plants were working as designed; the rest ran irregularly or not at all [22].

The result on the U.S. side is a beach that is often closed. On 3 September 2024 the Imperial Beach shoreline passed 1,000 consecutive days closed [23].

The hidden side: air, and the people who train in it

The water does not stay in the water. In 2023 Scripps researchers Matthew Pendergraft, Kimberly Prather and colleagues found that up to three-quarters of the bacteria in Imperial Beach's coastal air came from sewage-polluted water thrown up by the surf. The authors were careful: the study did not show that anyone was made ill [24].

The sewage also gives off hydrogen sulfide, the gas behind the smell of rotten eggs. On 19 March 2026 it reached about 500 parts per billion near Imperial Beach schools, more than 15 times California's one-hour standard of 30, according to CalMatters. The air district paid for 199 air purifiers for local schools [25]. In October 2024 county and CDC interviewers surveyed 189 households in Imperial Beach, Nestor and San Ysidro. Ninety-five percent said they had smelled sewage in the previous 30 days (Map 2) [26].

A South Bay pediatrician, Dr. Vi Nguyen of Kaiser Permanente in Otay Mesa, has described more asthma, pneumonia and headaches among the children she treats. She has spoken on the record but has not published figures [27][28]. One peer-reviewed study, in the Western Journal of Emergency Medicine in 2025, found that emergency visits for diarrhea at a nearby hospital tracked the river's flow in summer 2023, rising to more than three times the weekly average after Tropical Storm Hilary [29]. No published study yet measures children's health here. The county began an exposure study with UC San Diego in 2026 and plans a retrospective study of hospital, cancer and death records [30].

The same water runs past Naval Amphibious Base Coronado, where candidates for the SEAL teams train in the surf. The Pentagon's Inspector General reported in February 2025 that from February to September 2024 about three in four water tests off the base exceeded state standards, and that 12 of 265 water-training events, about 5 percent, were moved. From 2019 to 2023 the command diagnosed 1,168 cases of acute gastrointestinal illness among candidates (Figure 2) [31][32]. The Navy agreed to set rules for monitoring the water and moving training. Whether it tracks what repeated exposure does to candidates is a question for Naval Special Warfare.

The bay side: the waterfront that had to be cleaned first

Six miles north, across the Silver Strand, lies a different body of water with a different problem. San Diego Bay meets the Pacific only at its mouth, between Point Loma and North Island (Map 3). Its southern shore, Chula Vista's bayfront, spent most of the twentieth century as industrial ground.

Rohr, the aerospace manufacturer, made aircraft components there from 1941 until it left in 2002. The regional Water Board's cleanup orders read like a solvent catalogue: trichloroethylene (TCE) and the compounds it breaks down into, 1,1,1-trichloroethane, hexavalent chromium, lead, cadmium and PCBs [33][34]. For TCE and PCBs alike, the federal health goal for drinking water is zero, and federal rules let ground where people will spend time keep no more than 1 part per million of PCBs without further controls [35][36]. In 1993 groundwater under Rohr's North Campus held TCE at 300,000 micrograms per litre, against a drinking-water limit of 5 (Figure 6) [34]. From 2020, on a parcel within the bayfront plan, contractors installed underground barriers of iron, vegetable oil and Dehalococcoides, bacteria that strip chlorine from the solvent one atom at a time until it becomes harmless ethene [34][37]. The board estimated the work its 2021 order requires at $18.7 million to $26.8 million [34]. Its 2014 order for the South Campus, at the foot of H Street, lists the people the cleanup must protect. Among them are future hotel guests [33].

Next door, the South Bay Power Plant ran for about five decades until the end of 2010 and was imploded in February 2013 [38]. The marshes at the bayfront's edge, now a national wildlife refuge, hold contaminated sediment from waste disposal and industry that began in the late 1800s [39].

By 2010 local press called the bayfront's redevelopment a "38-year effort" [40]. The California Coastal Commission approved the Chula Vista Bayfront Master Plan unanimously on 9 August 2012 [41]. On 15 May 2025 the Gaylord Pacific Resort and Convention Center opened there: about $1.35 billion by the Port's figure, 1,600 rooms and some 477,000 square feet of indoor and outdoor event space [42][43]. The San Diego Convention Center downtown has 615,701 square feet of total exhibit space; one hotel now sits in the same order of magnitude as the region's main convention venue (Figure 4) [44]. Chula Vista's mayor projects $475 million a year in economic activity [42].

So the bayfront arrived just as the sewage headlines peaked. The two are separate problems. One is legacy pollution, cleaned under orders; the other is a chronic discharge that is still arriving. From a distance they blur into one picture of the South Bay. On the map they are miles and a peninsula apart.

Both sides of the line

It would be easy to tell this as Mexico's sewage on America's beaches. The record does not support that. Mexico's acting foreign minister has said the heaviest concentration of pollution is on Tijuana's own beaches [45]. At Playa Blanca, beside the Punta Bandera discharge, enterococcus bacteria measured 10,462 per 100 millilitres on 31 July 2025, against a Mexican limit of 200 [21]. People born in the United States are the largest group among Mexico's foreign-born residents [46]. Margarita Díaz of Proyecto Fronterizo de Educación Ambiental put the gap plainly to the Tijuana weekly Zeta: the United States is meeting its dates, and Mexico is behind [21]. Mexico's commitments under the 2025 agreement, backed by $93 million left over from a 2022 pledge, are due by the end of 2027 [47].

Inside one country, a dispute like this goes to court, and on the U.S. side it did. In 2018 Imperial Beach, Chula Vista and the Port of San Diego sued the U.S. section of the boundary commission; San Diego, the Water Board, the State Lands Commission and the Surfrider Foundation followed. The suits settled in April 2022 [48]. Across the line no court has authority over both sides. There is a treaty minute and a calendar (Strip map).

Feared, then played down

This coast has had a sewage emergency before. On 2 February 1992, at the northern end of the same shoreline, the Point Loma outfall, the pipe that carries San Diego's treated sewage offshore, broke about 3,000 feet from shore in roughly 35 feet of water [49][50]. For about two months nearly 190 million gallons a day poured into the kelp forest instead of deep water [51]. Scientists feared for the forest. When Mia Tegner, Paul Dayton and colleagues studied it, they made the question their title: catastrophe or disturbance? Near the break the kelp suffered. Beyond a kilometre, the extra nitrogen fed a canopy starved of nutrients, and after the repair the hardest-hit zone grew back as dense forest. They called it "a modest disturbance" [51].

That spill was sudden and short, and was treated as an emergency. The flow at the border has run for decades and been treated as a chronic condition (Figure 5). The fixes now under way, from the expanded plant to the river diversion, are real and scheduled. Whether the response matches the scale is for readers to weigh against the figures. Several questions remain open: what the county's health studies find, what the Navy measures, and when Imperial Beach's closures stop being counted in years.

One shoreline, two trajectories

From a distance, all of it is one stain: a closed ocean beach, a century of industry on the bay, a city across the line. The word that carries it is pollution. It is accurate, and it is too large to act on.

On the map it comes apart. The bay's problem is old and fixed in place. Its solvents and metals were left by industries that have gone, and they are being cleaned under state orders, parcel by parcel [33][34]. Beside those parcels a 1,600-room resort opened in May 2025 [42][43]. That trajectory is legible: a legacy, a cleanup, a reuse.

The ocean's problem arrives new each day, with the river's flow and the discharge at Punta Bandera, and it ignores the boundary that every fix must respect. Its trajectory is a schedule: 35 million gallons a day reached in 2025, a larger plant designed, a treaty minute signed [17][18]. Even a schedule kept is not the end. Studies of beaches elsewhere find that fecal bacteria persist longer in sand than in water [54]. No one has published what the sand at Imperial Beach holds, or how long it would take to clear once the flow stops.

Seen from farther away, the separation disappears altogether. In December 2025 the county kept an advisory on the Children's Pool in La Jolla, a harbor-seal rookery [55]. On 9 May 2026 it closed the Campland shore of Mission Bay, citing runoff from a fire that morning at a neighboring boat club [56]. The same December week, the shoreline from the border to the end of Imperial Beach's Seacoast Drive was under a sewage advisory [55]. Three places, three notices, and where a cause is named, it differs. And after every heavy rain the county advises people to stay out of the whole coast, from San Onofre to Border Field and both bays, for 72 hours, because of urban runoff [57]. A reader in another state could see one headline: San Diego's beaches are closed again.

What rides on that headline is large. The coast is the region's postcard, the one this essay began with, and visitors spent $14.4 billion in San Diego County in 2025, by the tourism authority's count [53]. The region on both sides of the line holds more than six and a half million people (Figure 3). It financed a $1.35 billion resort on its bay; EPA's 2021 capital estimate for the comprehensive fix was $627 million (Figure 4). Both are nominal and given for scale only. What the closures have cost, in visits, property, health or training, has not been counted, and this report does not guess.

The Hotel del Coronado stands at the northern end of the same closure shoreline (Map 2), and the bayfront that spent decades getting clean sits a peninsula away. Whether repeated headlines change how people see them, and how long a reputation takes to recover once the water does, is not measured either. The people who live along this shore have answered a simpler question. In the county and CDC survey, 95 percent of households said they had smelled sewage in the past month [26].

A closure notice is local; the headline is not. Where do these stories travel, and do they reach the places the region invites people from: the visitors, the students, the young workers recruited on the promise of the coast? Those questions are for a follow-up.

Sidebar: how the map separates what perception merges

The location desk built this piece the way it builds a map: data first, then judgement.

• Positions are tiered. Each of the 41 plotted places carries its source: official coordinates (the City of San Diego's outfall inspection reports), an OpenStreetMap object, or a hand placement drawn as a hollow symbol and logged as approximate [52].
• The shore is measured. The closure shoreline on Map 2 was traced from the satellite image, scanning each row from the open sea to the first land, rather than taken from a generalized coastline.
• Water is drawn over pipes. Flows sit above the outfalls because the water moves above them, and every flow path is labelled schematic, not model output.
• Co-location is not cause. The bayfront's legacy and the ocean's plume lie near each other; nothing here claims one causes the other, and no illness is mapped.
• Every gap is written down. Positions still to verify, cleanup boundaries still to overlay and air-monitor sites still to add are listed as open walls at the back, so the next draft can close them.