Rare Algae Bloom Kills Hundreds of Fish at Spreckels Lake

By Carol Dimmick

Workers at Golden Gate Park responsible for maintenance at Spreckels Lake, a large pond in the northwestern section of the park, became alarmed in late June when hundreds of fish began washing up dead on the shoreline. “The fish were gasping for air,” said Chris Daquiozg, a gardener who works at the lake.
Unusually warm June weather proved deadly for hundreds of fish living in the algae-infested water at the lake. This is the second time in 10 years that fish have died in significant numbers at Spreckels Lake due to an algae bloom.
According to John Farley, a SF Recreation and Park Department supervisor at Golden Gate Park, about 80 large carp and hundreds of smaller fish died during the hot spell. Farley said that as the fish continued to wash up on shore, park personnel became concerned and turned to the California Academy of Sciences for answers.
Patricia Morales, a pathologist at the Academy, was asked to analyze specimens from the lake. She found that a variety of factors led to an ecological meltdown at the lake.
According to Morales, the fish died when the hot weather triggered an algae bloom which depleted the oxygen supply in the water. But she also says a lack of circulating water and an overabundant fish population helped to turn the large pond into a death trap.
Spreckels Lake, like many lakes and ponds in the city, has become a dumping ground for unwanted pets and freed animals that were slated to be used as food. Due to an absence of natural predators, the abandoned fish have multiplied over the years until the small lake can no longer accommodate their numerous offspring. “
The lake could no longer handle the biological load .... Ironically, the death of the fish is good for the health of the lake,” Morales said.
As a short-term solution, in mid-July workers at the lake sprayed Aqua Shade, a nontoxic pesticide, into the water to neutralize the algae. According to Morales, the chemical works by reducing the light that triggers algae growth.
At the same time, water circulation was increased by opening intake valves to an underground well that supplies the lake with water. But these measures are only short-term solutions and a more comprehensive approach is necessary to stabilize the water.
“ In the long run we need to look at the whole lake system. One of the considerations is an air circulation pump or fountain,” Farley explained.
A pump for Spreckels Lake would cost about $4,000. But any long-term solution for Spreckels Lake will have to wait until a team of experts finishes evaluating all the ponds and lakes in Golden Gate Park, a process that is now underway.