Mixed stratified water and blooming algae are the suspected culprits in a massive die-off of fish in The Lakes at Rancho El Dorado, a not uncommon result of monsoon runoff.
Some residents estimated 2,000 dead fish. Resident Tod Antell said residents were very upset with the sight and the smell.
“It’s an ungodly smell. You can’t walk out and breathe correctly,” resident Danelle Mayfield said. “There’s probably close to 800 plus fish in my visual view of what I’m seeing on my little part of the lake. The ducks are not even getting in the water. They are staying on the shore at this point. There’s still multiple fish gasping for air.”
The situation was noticed last week during monsoon rains.
Megan Perry, a Maricopa resident who worked for U.S. Fish & Wildlife Services, took a look at the situation and believes the monsoons played the biggest part in the die-off.
“It’s natural and nothing to panic about,” she said.
In summer, water levels stratify in lakes, she said, with warm, low-oxygen water on the bottom and cool, higher-oxygen water on top.
“When an event happens like a temperature shift or monsoon or even sometimes an algae bloom, the warm low-oxygen water on the bottom and cool, denser water on the top suddenly mix as they try to switch places,” she said. “This causes the oxygen levels overall to suddenly fall, suffocating the fish and causing a large die off.”
The fish, other than being dead, look to be in normal health, with no indication of poisoning or other unnatural cause, Perry said. She noted the small minnows are still alive because they live closer to the oxygen and have less oxygen demand.
Meanwhile, monsoons can also cause algae bloom, which can be fatal to fish as well when soil is washed into the water. The soil creates an overload of nitrates. Algae bloom, eat the nitrates and then die. Bacteria devour decaying algae and, in the process, use up much of the oxygen in the lake.
That kills the fish.
In the Lakes, it was apparent some fish were dying last week. By Monday morning, the result was thousands of dead fish, affecting every reach of the lake.
H2Ology, the company hired by the HOA to take care of the lake, said these kinds of fishkills are “an unfortunate part of ornamental lake systems in the summer.”
Mayfield, the resident, said she had contacted the homeowners association, Associated Asset Management, which is responsible for the lake conditions.
“I contacted the HOA emergency line last night,” she said. “They said that they would be dealing with it today. I have contacted Fish and Game Department. They advised that the HOA needs to deal with it. I have contacted the company that handles the water for the lakes and they stated that they are taking care of it. I have contacted the health department and also, again, the HOA today. I left a message again; no call backs. As of right now, we have not seen anybody coming out to address any of the issues so far this morning.
“We haven’t had anything like this. I know one of the other neighbors was talking about it and they’ve lived here six years and they’re all on the water, too, and they’ve never seen anything like this.”
Perry, the local fish expert, said water features can help mitigate the situation.
“Those fountains like those you see at the entry of Rancho El Dorado and the Villages, they’re are not just for show,” she said. “They help aerate the water.”
The Lakes does use landscaped water falls and other aerators in some locations to churn the water, when they are functioning.
According to H2Ology, a crew will be removing all the dead fish that have surfaced today, and “measures will be taken to stop future kills.”
Staff reporter Michelle Chance contributed to this story.