A knotty old problem: Water exchange and circulation are widespread challenges in human-made lagoons. They have plagued Aquatic Park since shortly after its lagoons were created during the Great Depression — to solve an even worse problem. The park has long seen smelly algae blooms, mass die-offs, pollution, and sediment gradually shallowing the lagoons. Climate change promises additional difficulties from rising sea levels, more and longer droughts, and storms that dump more water than the city’s storm drains are designed to handle.
Since the 1980s, increasingly detailed studies have recommended solutions. None has led to action. Most solutions would be expensive and complex, besides construction requiring difficult permitting and agreements with the railroad and CalTrans.
The lagoons cannot simply be opened to Bay tides. Tidal rise and fall must be limited because several buildings are close to or even below Bay high-tide levels. The Bay’s twice-daily tidal rise and fall, often of six feet or more, also would make boating unattractive and risk miring folks on mud flats. For these reasons, fluctuations in Aquatic Park’s main lagoon are kept to about two feet at most. (They can be greater in the Middle Lagoon/Model Yacht Basin and less in the South/Radio Tower Lagoon.)
All studies have recommended regular maintenance of the existing tide tubes — pipes that carry water between Bay and lagoons or between lagoons. Instead, these connections have deteriorated. Several are broken or partly or entirely blocked. Some were cleaned about 2011 and in 2020 (using bond funds meant for capital projects). As of 2024, Berkeley is seeking federal grant funds to maintain or rebuild the tubes.
A web of tide tubes and storm drains:
Movements of water into, out of, and among Aquatic Park’s three lagoons are complex, varying with tides, rainfall, and water levels in the Bay and lagoons. There is no easy way to predict or diagram them. The sections below offer basic explanations, discussing the lagoons from south to north.
The image below shows the major water movements to or from land and Bay. It omits small drainages that bring urban runoff from neighboring roads or buildings, recent installation of permeable features from Allston to about Bancroft as part of building the new Berkeley Commons lab building, and planned trash separators east of the tracks plus a large bioswale at Channing, where another lab development may be in the works.
The South, Radio Tower Lagoon (or pond)
The smallest pond is easy to miss. Its south is a privately owned, site of a historic radio tower and station. Its northern portion, though part of the park, is largely cut off by a freeway entrance road and fencing to protect black-crowned night herons that sleep in daytime in shrubby willows along the shoreline. Shallow and seldom disturbed, it is a haven for other birds as well. CalTrans intends to someday abandon the substandard entrance road, enlarging the park — but has taken no action for years.
This pond also lacks water connections to the other two. Maps show only two pipes: a local storm drain from the freeway exit road at the southwest corner and a connection to the Bay at the northwest corner. This pipe is reported to have partly collapsed more than a decade ago, but water still moves through it in both directions. At very high and low tides, flows can be seen into and out of the pond, circling a marshy island in varied ways that suggest more than one connection, or perhaps a break in one.
Despite shallow, sun-warmed water and what looks like little water exchange, this lagoon does not seem to be plagued by the algae blooms that afflict the much larger main lagoon. This may be because it receives little nutrient-rich, fresh rain runoff from the land.
Left below, sparkling Bay water wells up in marsh vegetation in the south, Radio Tower lagoon. Right above, pipe box above NW corner of Radio Tower lagoon shows its location, above a loop channel in marsh vegetation. Right below, the pipe (yellow arrow) empties into the Bay a short distance south of the big Potter drain (red arrow). In this photo, at very low tide with no rain, the Radio Tower pipe has strong outflow while the Potter Drain is still.
The Middle/Model Yacht Basin Lagoon and Potter Drain
The middle lagoon is divided from the others by the freeway entrance road to the south and the loop road/trail around the main lagoon (Bolivar Drive) to the north. Shoreline terraces built from broken concrete, as well as a porthole-style window in the wooden building facing the lagoon, show that the Works Progress Administration’s Depression-Era workers intended this lagoon for the then-popular pastime of racing model sailboats.
As the Google Earth image left shows, the Model Yacht Basin is now too silted in for these races. Light-colored areas in the satellite image are shallows, some of them islands at low tide. The main lagoon, above it in the image, has no such shoals.
The giant Potter drain: Much of the material filling the lagoon comes Berkeley via the huge Potter storm drain, nine feet square. It channels rain runoff from more than a third of the city, most of south Berkeley, toward the bay — with significant spillover into Aquatic Park.
The drain runs mostly underground on the north side of the freeway entrance road (visible at at the bottom of the satellite photo). But pipes and grates open part of the drain to the Model Yacht Basin. Slide gates built to limit flows into the lagoon appear to be permanently open. As the photos below show, two large tubes visible at low tides, as well as open grates above the drain, can channel water, mud, and gravel into the pond during many, perhaps most, rains. Like other urban runoff, this contains pollutants including gas, oil, heavy metals, fecal bacteria, plastics, and chloraminated drinking water toxic to aquatic life. The city does not test water quality in this lagoon.
Below, tubes from Potter Drain to middle lagoon, visible at low tides. Left, streaks appear to show outflow from drain to pond during rain. Part of the flats near the drain can be seen in the foreground. Right, the same tubes with water flowing from pond to drain during a minus (very low) tide.
Dredging appears prohibitively expensive. Lessening pollution may be even more difficult. Much of Southwest Berkeley is not far above sea level. When high tides bring Bay water up into the Potter Drain, rain runoff loses this escape route and can flood streets or buildings. Climate change seems likely to worsen problems by bringing both sea-level rise and downpours larger than those the city’s storm drains were built to carry. One possible solution is pumps to force runoff out faster. Besides costs, however, these require maintenance — not a Berkeley strength. Power to operate pumps also can be lost in emergencies.
The openng in the drain has a silver lining. At high tides in dry weather, salty Bay water flowing up the Potter Drain floods into the small lagoon via the tubes and grates, bringing fish and other Bay life with it. The shallows that sediment has built become a magnet for fish-eating birds — herons, egrets, cormorants, gulls, pelicans, and more. Refreshment from salty Bay water also may be a reason that big algae blooms seem less common here than in the main lagoon.
Below: At very high tides, Bay water fountains out of the grates above the Potter St. drain, left, and roars out into the lagoon, right.
The pipe to the Bay: The WPA built a 24″ concrete pipe near the middle of the Model Yacht Basin’s west shore to bring Bay water in and take lagoon water out. This pipe has largely silted up — but some water muscles through anyway. As the photos below show, the force digs a pit in the lagoon’s sediments, with a bar around the pit. When the lagoon’s water level is low, you can see the outgoing whirlpool or incoming boil. On the Bay at low tide, you can see water bubbling up through the sand from the pipe’s outlet, well out in the Bay.
Below, left to right: At low water and incoming tide, water boils up through the heavily-silted pipe that connects the middle lagoon to the Bay via the concrete box at left. The broken pipe is an old drain from the freeway. Second from left: The 24″ pipe looms underwater toward the hole it keeps open. A small whirlpool shows outgoing flow. Right two photos: At very low tides, water can be seen boiling up from the buried mouth of the pipe from the Model Yacht Basin, well out from the Bay Trail and riprap.
Pipes between Model Yacht Basin and main lagoon: Another result of Potter Drain flows is that water levels in the Model Yacht Basin often fluctuate more and faster than in the main lagoon. This is important in exchanging water between the two lagoons.
Large concrete boxes on the north shore of the Model Yacht Basin mark locations of two 18″ concrete pipes built to carry this exchange. The eastern one still carries significant amounts of water, despite breaks and siltation. At right, water can be seen flowing from the east box into the Middle Lagoon/Model Yacht Basin. This shows that the water level in the main lagoon is higher.
On the other side of the road separating the two lagoons, the pipes project directly into the south shore of the main lagoon. When water is higher in the Middle Lagoon/Model Yacht Basin, you may spot a small whirlpool near the box and vigorous flow into the main lagoon. This draws egrets, herons, and diving birds including pelicans and cormorants, hunting small fish that come with the current or are disturbed by it.
The western pipe appeared completely blocked, with no visible flow at either end, until fall 2024, when a small current became visible flowing into the main lagoon. This may mean that tubeworms or other matter blocking the pipe have decayed or become loosened.
A 2007 memo modeling possible improvements to water circulation and exchhange between the two lagoons, done as part of the major, never implemented Aquatic Park Improvement Study, recommended replacing the failing pipes with a single bridge as the most cost-effective way of improving circulation.
The main lagoon
The main tide gates: mile-long main lagoon is busy with boaters, its edges popular for picnics, games, cycling, strolling, disc golf, wildlife watching, and more. Their enjoyment hangs on six tide gates near the middle of its west shore (left). Connected by pipes to the Bay, they are closed or opened to keep water levels from fluctuating more than about two feet. Without these gates, buildings near the shore would flood at high tides and boats would be stranded on mudflats at low ones.
Loss of this circulation would be catastrophic. The tubes are almost 90 years old. Their collapse would close the I-80 Freeway. Shutting off exchange with the Bay, it could lead to flooding of the main lagoon, adjacent roads and buildings, and nearby West Berkeley. The city has submitted a federal grant proposal to rebuild or improve these main tide tubes and those in the Middle Lagoon/Model Yacht Basin.
The lost north outlet: At the north end of this mile-long lagoon, an abandoned concrete box marks the Bay connection pipe that the WPA built. It was blocked long ago by the 1950s and 60s rush to fill the shallow waters west of the freeway. (Some water still seeps through, visible in a ditch in what is now McLaughlin East Shore State Park.) Limited circulation and exchange are likely reasons why dense, scummy algae sometimes covers much of the north and south ends of the lagoon, where inflow is limited. (The ends also are shallower and warmer, and may receive more fertilizing nutrients from urban runoff via the big Strawberry and Potter Drains.) For more on the roles of algae, runoff, and circulation, see See Change and Instability.
The Strawberry connection: Storm drains play a complicated role in the main lagoon, just as in the middle lagoon. The city’s second-largest storm drain roughly follows the old path of (mostlyburied) Strawberry Creek down University Avenue, reaching the Bay at a small cove just west of the freeway. But like the Potter drain, the Strawberry drain can flood low-lying property in heavy rains and high tides. To avoid this, a connection between the Strawberry drain and Aquatic Park is all but hidden near the end of Addison Street. Inside the piping, a weir –kind of low dam designed to let water flow over its top — keeps Aquatic Park from draining into Strawberry Creek, while also letting water flow into the park when the drain fills. At very high tides, current can be seen shooting out into the north end of the lagoon, often with birds lying in wait, diving, or hunting on the wing for small fish. In storm season, this flow brings silt and polluted runoff from West Berkeley.
Below: Cormorants dive for fish in flow from the Strawberry Creek drain outlet at the north end of Aquatic Park’s main lagoon. Pelicans, herons, egrets, and terns are often hunt here during inflows.
Mini-watersheds along the east shore: Multiple small and complex sources of runoff and pollution come from the streets a few blocks east of the park, between the big Potter and Strawberry drains.
One significant source is from Parker Street south — the long red line east of the main lagoon, shown on the diagram near the start of this page. As environmental laws and citizen interest strengthened, beginning in the 1970s, a pipe was built with the stated aim of intercepting most of the polluted far-western runoff from Parker Street south before it reached the main lagoon. This pipe was to carry it to the Bay via the Potter Drain.
As we have already seen, however, some of the Potter Drain runoff winds winds up in the middle lagoon via the big open pipes and grate on the south shore. In addition, the drains to the main lagoon were left in place when the bypass was built. At Heinz and Grayson, high tides moving up the Potter Drain also continue north into this pipe. In the rainy season, this pipe also carries polluted Potter Drain water directly to the main lagoon.
Below left: At very high tide, flow shoots forcefully and noisily from below Heinz Street directly into the main lagoon. This pipe also can bring storm water from Heinz itself or from West Berkeley via the Potter Street Drain. Below center: Old stormwater infrastructure from Grayson to the Aquatic Park main lagoon. Below right: A ditch (dark area) in the sediment in front of the Grayson Street drain seems to show that water sometimes flows forcefully into the lagoon here.
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