Report: Menifee Lake Fish Kill Attributed to Toxic Algae

The south end of Menifee Lake was clear of dead fish Friday afternoon -- a week after thousands of fish died there.

Additional tests of the water in Lake Menifee showed high levels of toxic algae that is considered to be the cause of the death of thousands of fish since the end of April, the lake manager said today.

Ken Durante has prepared a two-page report of the test findings that is available to Menifee Lakes residents in the lake office and will be included in the next newsletter of the homeowners association in that private community. It describes the presence of Prymnesium Parvum – commonly referred to as golden alga – in the lake.

Menifee 24/7 has viewed the report from Aquatic Consulting & Testing, Inc., the Arizona lab to which water samples were sent last week when several species of fish continued floating dead to the surface (below). According to the report, “golden alga was detected and dominant in the samples tested.”

According to the Arizona Department of Game and Fish, golden alga is rarely found in California lakes but has been responsible for many fish kills in Arizona and Texas lakes. This alga is a tiny, one-celled aquatic organism propelled by two “tails”, called flagella, that help it move through the water.

As described in Durante’s report, golden alga release toxins that affect gill-breathing aquatic organisms. In a bloom situation – which is consistent with current climate and weather conditions – enough toxins are released into the water to kill fish in great numbers.

According to the report, the toxins cause fish gills to lose their ability to exchange water and absorb oxygen. Fish then die of asphyxiation. An algae bloom was traced to April 26 – the day before fish began dying.

Tests of the water showed more than sufficient levels of oxygen in the water, which seemed to disprove a rumor that a newly installed aeration system is faulty. The oxygen level was measured at 10.8 parts per million. Anything above 4.0 ppm is considered safe, according to the report.

Those tests also showed no presence of deadly chemicals, which some speculated were introduced to the lake when the pool was drained.

But when fish continued to die, Durante said he began to suspect something other than the initial theory of drastic changes in water temperature. He said one of several experts who contacted him suggested the water be tested specifically for golden alga.

“It’s rare in California, but he said it sounded extremely similar to a situation where they lost an entire lake full of fish because of golden alga,” Durante said. “We sent some samples to be tested for that and they came back positive.”

According to the website stewardsofwater.com, golden alga has been identified as the source of fish kills in some California lakes in recent years. The Arizona Department of Game and Fish reports that the toxins produced by this alga have no apparent lethal or harmful effects on animals that do not breathe through gills. They also are not considered a public health threat.

“Healthy fish caught from infested waters are safe to eat. However, Menifee Lakes Rules and Regulations state that Menifee Lakes and the Lake Manager of Menifee Lakes do not endorse or recommend the eating of fish caught in Menifee Lake,” Durante wrote in his report.

“Now that I know what caused this, I have taken counter measures and treated the lake for it,” Durante said. “I will continue to monitor the lake and send monthly samples to this Arizona lab to ensure we have eradicated the alga and it has not come back."

Durante said the California Department of Fish and Game was not involved in the investigation because Menifee Lake is a private lake and not under DFG jurisdiction.

Durante said the lake water was treated with algicide – standard procedure in treating this problem.

Further confirmation of golden alga as the cause of the fish kill could come when tests performed by UC Davis biologists on some of the dead fish are completed. Those results may not be available for a week or two.

Jackie Johansen, a Menifee resident with degrees in conservation biology and zoology, contacted the UC Davis biologists after studying the effects on the fish. She was present when those biologists removed some of the dead fish on Monday for testing.

“They could tell the fish had suffered some sort of stress, but they couldn’t identify right away what it was,” said Johansen, who writes a “In the Wild With Jackie” column for Menifee 24/7. “But they know golden alga was present, and they know that has caused fish kills in other lakes. They are testing for that now.”

It is difficult to determine the origin of the toxic algae in Menifee Lake. Johansen said one factor that could’ve introduced foreign substances to the lake was the flooding from a winter storm that merged water from Menifee Lake and The Lakes body of water across the street.

“I personally observed the newer, upper 'Lakes' draining into the older, shallower Menifee Lakes down below,” Johansen said about the flooding several weeks ago. "At that time, there were hundreds if not more fish that were washed, along with dirt and debris, into the lower Menifee Lake.

“Menifee Lakes had many fish die off, but the Lakes, which is right next door, did not. What would make this happen? Keep in mind the difference in the sizes and builds of these two lakes. Menifee Lakes is almost 25 years old, and it is only about 17 feet deep. The newer “Lakes” is less than 10 years old, and it is 75 feet deep. If you have ever dealt with fish tanks, you know that the larger the fish tank, the easier it is to keep it healthy.”

Johansen said it is possible that The Lakes contains golden alga that hasn’t had a deadly effect on fish because of the size and depth of that body of water.