On Tuesday, Southside Park's pond glimmered clean and clear. Only a hint of the smell of dead fish and algae remained.
A few amateur fishermen were out trying their luck on the south side of the pond at Eighth and T streets. But the north bank had some reminders of last weekend's fish kill, where a hundred small bluegills and a dozen catfish and carp lay lifeless and decaying, blown into the marsh.
Experts attributed the kill to fish being deprived of oxygen following record heat last Friday and Saturday and a large algal bloom.
Residents complained of unsightly white pond scum, and an overpowering smell of garbage and rotting fish.
Tony Ulep, a park supervisor, said Tuesday that he has seen about half a dozen fish kills at Southside Park's pond, also during times of extreme heat, but none compared to last weekend. "The smell was the worst I've ever experienced. And I've been here 13 years," he said.
Ulep is in charge of cleaning up the shoreline each time a fish kill happens.
"It was hundreds yesterday. My guys took out two garbage cans that's 55 gallons of fish each just on the shore," he said .
Nann Fangue is a biology professor at UC Davis, whose research involves understanding how fish survive in complex environments.
Fangue said hot weather spelled a death knell for fish: Water holds less oxygen when it's warmer. Unfortunately, high temperatures also increase the metabolic (or oxygen) demand of fish.
Algae are plants, and they give off quite a bit of oxygen during the day. At night, however, algae switch to respiration: They take in oxygen and expel carbon dioxide, just like humans. "You can have dramatic oxygen level shifts from day to night," Fangue said.
The health of the pond is under the city's jurisdiction. The fish are not stocked by the city, but by the state's Department of Fish and Wildlife. DBI Services, hired by the city about a month ago, is in charge of controlling and monitoring algae in the pond. "It's kind of a weird setup," Ulep said.
An algal bloom was suspected and reported on Memorial Day week. DBI Services found a bloom of planktonic algae, commonly referred to as "pea soup." Last Thursday, the firm treated the pea soup with cutrine. "It's the safest product to use on algae," said David Najera, who works for DBI Services.
On Sunday, local residents reported that the algae was white in color. However, live algae has chlorophyll in it and is green, Fangue said.
She said the fish kill could be related to death of the algae itself. Algal blooms naturally follow a boom-and-bust cycle. As they die, they rapidly deplete oxygen, Fangue explained.
"They'll proliferate, and then you'll have this massive die-off, or maybe the city killed them, and that can lead to a low oxygen event and a fish kill," Fangue said.
The algae itself is not necessarily bad, said Fangue. She said algae "stinks, but it shouldn't necessarily kill fish. Lack of oxygen is what killed the fish."
"I don't know why they want to kill the algae in general, because it's not hurting anything. It's probably just that people like to look at clean stuff, and not look at stagnant stuff."
Fangue recommended installing a fountain to provide oxygen even at night and reducing inputs that lead to algal blooms, such as fertilization. But Southside Park hasn't been fertilized in years, Ulep said..
Najera added that algal blooms are caused by a variety of things in the environment, particularly people throwing food in ponds and nutrient-rich excrement from waterfowl.
Najera said it is critical that people do not feed the ducks. "High loads of phosphorus come out when they poop," he said. Ducks should naturally be a migratory animal, but feeding encourages them to remain in the area, he said.
When Ulep, a Marine reservist, left to serve in Iraq in 2009, he had 20 employees to maintain 17 parks. He returned home in 2011 to find his crew decimated by city budget cuts. He now has nine workers for 38 parks.
Despite these setbacks, and with the help of volunteers, Southside Park has come a long way.
"It's good to see the community coming together now," Ulep said. "People are taking ownership of their park. I am thankful to every volunteer who comes here."
Najera said he's committed to preventing another fish kill. We've submitted data and a plan, and we're hoping to find one that works for the city," he said.
Call The Bee's Ellen Le, (916) 321-1031.