Change and Instability

Aquatic Park’s lagoons look peaceful, but like most human-created lagoons, they undergo quick changes that can devastate plant and animals and disturb visitors’ enjoyment. Things may be made worse by freater storms and droughts and other climate-related changes, along with the gradual filling of the lagoons by polluted runoff from much of Berkeley.

Inadequate circulation and exchange with Bay waters have been problems almost since the park was created during the 1930s — as an afterthought to building a highway to the Bay Bridge. In the 1950s and 1960s, Berkeley came close to letting the lagoons be filled for industrial expansion. As environmental awareness grew, pollution, smells, algae, and repeated die-offs led to increasingly expensive studies, all recommending reducing polluted runoff from the city and improving circulation and exchange. None of these studies led to significant action. Meanwhile, the city failed to maintain the pipes connecting lagoons and Bay.

By 2020, invasive Australian tube worms (Ficopomatus enigmaticus) had all but blocked the tide tubes between the Bay and the main lagoon. The city used bond funds meant for capital improvements to clean the main tide gates and tubes, restoring some rise and fall of tides.

An excellent 2020 YouTube video on the worms is here (this will open in a new tab)

Two years of drought followed the cleaning, with few obvious problems:

Dead Australian tube worm casings blocking Aquatic Park tide tube — In summer 2022, casings of dead Australian tube worms still blocked smaller connections and lined much of Aquatic Park’s main lagoon, although the worm cases were crumbling. Live worms may have died because of greater rise and fall of tides after the main tide tubes were cleared. The photo shows the blocked western pipe between the main and middle lagoons — one of two critical for water exchange. Only in the summer of 2024 did a small stream of water begin to be visible through this pipe.

Dead native oyster shell bottoms — In summer 2022, casings of dead Australian tube worms still blocked smaller connections and lined much of Aquatic Park’s main lagoon, although the worm cases were crumbling. Live worms may have died because of greater rise and fall of tides after the main tide tubes were cleared. The photo shows the blocked western pipe between the main and middle lagoons — one of two critical for water exchange. Only in the summer of 2024 did a small stream of water begin to be visible through this pipe.

Dead mussels, Aquatic Park — **By late spring 2023,** gaping shells showed that massive numbers of mussels also had died (above). Mussels, important in filtering out pollutants, can tolerate difficult conditions, but not extremely long stints in fresh water. Those nearest the tide gates, where saltier ay water flowed in and out, seem to have survived.

Algae and widgeon grass at north end of main lagoon — **As spring 2023 turned to summer,** algae and widgeon grass covered significant areas at the north (above) and south ends of the main lagoon, where circulation is limited.
Though not toxic, this dense algal growth can shade out sunlight and leave water without oxygen, killing other life. Widgeon grass is a native aquatic flower plant that ducks love. But it hinders boaters.

Below: Thousands of tiny Asian date mussels, an invasive species, rested on the algae dense algae.

Yellow-green algae, bubbles, and invasive Asian date mussels

These blooms are now new. As in the past, the city paid a harvest boat, visible in the background below, to cut the algae and wigeon grass and haul it ashore. Otherwise, the mass would stink before it sank — speeding the shallowing of the lagoons.

Through a second rainy winter in 2023-4, and a cool, late spring, massive quantities of urban runoff as well as salt Bay water at high tides flowed into the lagoons via the Potter Street storm drain edging the Model Yacht Basin and the Strawberry Creek connection at the north end of the main lagoon (see Connections and Circulation).

April 2024 brought a brief, massive bloom of slimy filamentous algae, typical of eutrophication, in the Model Yacht Basin/middle lagoon, covering large areas in early April before disappearing almost overnight. It did not recur all summer. This bloom seemed to be new. There was no such algae in the main lagoon, and there had been virtually no such algae in this smaller lagoon the previous summer, during the main lagoon’s massive blooms. No one seems to remember this kind of bloom in this pond before in any season. (If you remember or know about such blooms, please email f5creeks@gmail.com).

This lagoon seems to be filling in, with much of it shoal at lowest tides. Sunlight through shallow water could promote the growth of algae, but cold, cloudy Bay water flooding in from the huge Potter drain at high tides may limit this growth.

Model Yacht Basin looking SE from western pipe-connection box on N shore — /Algae in Model Yacht Basin, looking east from W. pipe box on N. shore, April 8, 2024

Algae in Model Yacht Basin, April 2024, looking S. from western pipe box on N. shore. — /Algae in Model Yacht Basin, looking east from W. pipe box on N. shore, April 8, 2024

Algae in Model Yacht Basin, April 8, 2024

In summer 2024, there was almost no surface scummy algae, perhaps due to late rains, relatively cool temperatures, or an overall lack of deluges or heat waves. In the main lagoon, however, the bottom visible from shore tended to be dense with scummy, thready algaes, especially at the north and south ends. Along with them came seaweeds that have spread worldwide, thriving in shallow, muddy estuaries with sharply changing temperature and salinity and high levels of nutrients from land runoff.

These can be signs of eutrophication, a vicious circle: Too great load of nutrients promotes growth of algae and other plants. Although these can provide habitat and food, they also can deplete oxygen, kill fish, acidify water weakening shellfish, and promote algae that carry toxins. Loss of mussels and other filter-feeders means they no longer purify water. As the algae decays and sinks, it hastens the natural filling of ponds, which become marshes and then dry land.

On the positive side, mussels showed signs of making a comeback. There were some large crabs, including the voracious, invasive European green crab, along with tentative first sightings of sharks and bat rays since the die-off in the winter of 2022-23. For more on animals in the park, see the page Hidden Creatures of the Lagoons.

Scummy algae in clear water, E. shore Aquatic Park — Water in the main lagoon was mostly clear in summer 2024. The thready algae that dominated the shallow bottom could be seen a long way out.

Cloudy, pea-soup-like water near Strawberry Creek overflow outlet — Where a sill in a buried pipe lets high flows from Strawberry Creek spill into the lagoon, water for some time remained a pea-soup cloudy green, with a blackish, scummy mass floating at the outlet. This suggests a possible bloom of bluegreen algae. It could be related to water trapped in the connecting culvert.

Scummy filamentous algae, Aquatic Park, summer 2024 — Green, tan, or brown thready algae dominated especially the north and south ends of the main lagoon. The shiny green wigeon grass shown in this photo was rare in 2024. It abounded in 2023, but was overgrown by surface scum and mowed.

Small brownish seaweed, most common species in 2024 — Algaes that have a structure are called seaweeds. This small, brownish seaweed was by far the most widespread in the main lagoon, covering large areas. It is probably “worm wart weed.” Seaweed ID is difficult: Species have spread and mixed worldwide, and traditional identifications often don’t mesh with modern genetics.

Clumps of small red "succulent seaweed." — The second most common in 2024, one of a group called “succulent seaweeds,” also has spread worldwide into shallow estuaries with tough conditions.

Dead man's fingers, a green algae common in Aquatic Park's lagoons — “Dead man’s fingers,” larger than those above, grows fairly commonly in scattered clumps. It probably spread worldwide with shellfish culture and trade.

Sargassum muticum, Japanese wireweed — Another relatively large seaweed, Japanese wireweed, has caused problems for wildlife and shipping with massive blooms — though not yet in the Bay Area. Like dead man’s fingers, it is most common in the central lagoon, fairly near or across from the main tide gates.