A knotty old problem: Water exchange and circulation are widespread challenges in human-made lagoons, and have been challenges since shortly after Aquatic Park’s lagoons were created during the Great Depression. Problems include 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 are more 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: This page focuses on the complex movements of water into, out of, and among Aquatic Park’s three lagoons.
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, as well as slightly larger “micro-watersheds” from about Allston to Channing, where changes are proposed or under construction.
These movement are surprisingly 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 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 is part of the park, but largely cut off by a freeway entrance road and fencing that protects black-crowned night herons that sleep through their days 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.
The Model Yacht Basin, in the lower part of the Google Earth image left, is now too silted in for races. Light-colored areas in the satellite image at left 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, built to channel rain runoff from more than a third of the city, most of south Berkeley — to the Bay.
The drain runs on the lagoon side of the freeway entrance road (visible at at the bottom of the satellite photo). However, slide gates built to limit overflows into the Model Yacht Basin appear to be permanently open. Thus, 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 many pollutants, including gas, oil, heavy metals, fecal bacteria, plastics, and chloraminated drinking water toxic to aquatic life. The city does not test the 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 South Berkeley is not far above sea level. When high tides bring Bay water up into the Potter Drain, rain runoff loses its escape 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.
There is a silver lining. At high tides in dry weather, salty Bay water flowing up the Potter Drain can be a boon. It 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 affects how water moves 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 exchange water between the middle and main lagoons. The west pipe appears to be completely blocked: No water movement can be seen.
The east pipe, however, carries significant flows in spite of breaks and siltation. When the main lagoon has the higher water level, current can be seen flowing from the concrete box straight out into the middle lagoon. More often, water is higher in the smaller 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.
Below left: Egret and cormorant fishing at the east inflow from the Model Yacht Basin to the main lagoon. Below right: Flow through what looks like two pipes, one broken at the top, excavates a channel for the water.
The main lagoon
Tide gates and the lost north outlet: Runoff pollution from the city harns water quality in Aquatic Park. The city tests the main lagoon weekly for bacteria that indicate pollution by animal waste, including humans. Because these tests fairly often exceed state standards, the city considers the lagoons suitable for recreation that involves limited water contact, such as boating, but swimming and fishing are prohibited. City policy is to post test results when there is a change, so available information may be out of date. To see the most recent posted report, go to this page and scroll down.
Nevertheless, the mile-long main lagoon is busy with boaters and 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. These 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.
At the north end of this mile-long lagoon, the Bay connection pipe that the WPA built was long ago blocked 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.) The neglected pipes linking the middle and main lagoons are discussed in the previous section, on the middle lagoon/Model Yacht Harbor.
Left below: Six tide gates close to the middle of the main lagoon’s west shore are its main source of Bay inflow. They are closed or opened to maintain water levels. Right below: Limited circulation and exchange are one likely reason why dense algae sometimes covers much of the north and south ends of the lagoon, where inflow is limited.
Algae and circulation: Limited circulation has a cost: In summer, thick mats of scummy algae can build up, bubbling, turning from yellow-green to black, smelling, even killing other life as the algae suck oxygen out of the water and rot. The algae is most abundant at the north and south ends of the lagoon — besides having limited circulation, both are shallow and easily warmed in summer. Dense growth also seems particularly likely after heavy winter rains that bring lots of fresh water and nutrients (nitrogen and phosphorus) from the land. This also encourages growth of widgeon grass, an aquatic flowering plant that boosts waterbird habitat but can support algae at the water surface.
The role of this runoff in mass die-offs is briefly addressed in the page Change and Instability.
Aquatic Park’s blooms have not (yet) contained toxins directly poisonous to other life, as has occurred in other parts of the Bay. Algae itself is natural and even beneficial, keeping water cool and providing food and cover for small creatures that feed larger ones. Excess, and our aesthetic preferences, are the problems.
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 will include polluted runoff.
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 also common feeders here.
Mini-watersheds along the east shore: Multiple small and complicated sources of runoff and pollution come from the streets a few blocks east of the park, between the big Potter and Strawberry drains.
From Parker Street south, the story begins with the long red line shown on the diagram near the start of this page, east of the main lagoon. As environmental laws and citizen interest strengthened, beginning in the 1970s, a pipe was built aiming to intercept most of the far-western runoff from Parker Street south. The idea was to channel polluted runoff to the Bay via the Potter drain.
As we have already seen, however, some of this runoff winds up in the middle lagoon instead. In addition, the drains to the main lagoon were left in place. At Heinz and Grayson, high tides moving up the Potter Drain also continue north into this pipe. At Heinz, they can shoot forcefully and noisily into the main lagoon. This almost certainly brings some polluted storm water in the rainy season.
Below left: At a very high tide, flow can shoot forcefully from the old drain west of Heinz. Below right: Old drain infrastructure in Aquatic Park west of Grayson, with a bit of the large concrete outlet pipe on the shoreline at bottom.
Farther north, from about Channing to Addison, construction and future plans make the fate of runoff too complex to cover now.
Check back for additions and improvements! Suggestions and corrections welcome!