Marin Civic Center lagoon fish kill blamed on algae bloom
By LORENZO MOROTTI | [email protected] | Marin Independent Journal
PUBLISHED: August 12, 2020 at 3:10 p.m. | UPDATED: August 13, 2020 at 2:13 p.m.
Algae bloom killed more than 100 fish in the Marin Civic Center lagoon, a state biologist said this week.
A California Department of Fish and Wildlife scientist met with Marin County Parks superintendents on Tuesday.
County staff took a sample of the water on Monday and shared it with the state, whose biologist determined that insufficient oxygen in the water resulted in an overnight event that killed masses of non-native fish, said Ken Paglia, a Fish and Wildlife spokesperson.
“So there was a heavy algal bloom prior to the fish kill,” Paglia said. “Our scientist said, ‘based on this information and my personal observations I believe it is a nighttime oxygen dissolve issue, which was exacerbated by the algal mats decomposing in the lake.'”
He said this can happen to warm-water fish such as carp, bluegill and bass in shallow bodies of water, adding that the waterfall and a fountain in the lagoon were inoperable for about a year and helped create the conditions for an algae bloom.
“When the fountains are operable they improve the oxygen levels,” he said. “This phenomenon occurs when oxygen dissolves in the water and causes fish kills. It happens from time to time but it’s not anything of concern.”
Staff is repairing a malfunctioning aerator and the fountain, looking into water control monitoring and identifying factors that led to the bloom, said Chris Chamberlain, assistant director of Marin County Parks.
“We are in the middle of getting that repaired, not pointing the finger to that but certainly any opportunity to improve oxygen circulation out there is going to be helpful,” Chamberlain said. “Most importantly is that lagoon is not designed to be a fish habitat.”
He said the lagoon was built to provide drainage for the parking lot and to complement the aesthetics of the Frank Lloyd Wright-designed Civic Center.
Over time, people have released non-native fish into the lagoon and created an ecosystem that was not envisioned when it was built, Chamberlain said. Waterfowl also contribute to organic matter that can cause algae blooms.
“Another contributing factor is low rainfall,” he said. “When we have good winters and runoff pumping into lagoon this doesn’t happen … when we don’t have a good winter it facilitates the organic matter build up, which is a key contributor to algae bloom according to the biologist. It is likely that brought the oxygen level down and created a toxic environment for the fish.”
While there are now fewer dead fish floating in the lagoon, Chamberlain said the county is keeping up signs warning the public to not allow pets near the water. More water samples will be taken to test if the water poses a threat to pets or people, he said.