Dozens of decomposing koi fish lay strewn along the banks of Fountain Hills famed town lake last week as buzzards picked away at their carcasses.
The centerpiece for Fountain Hills — a 28-acre man-made lake that features the world’s tallest fountain — had become overrun by too much algae, raising ammonia levels in the water and killing the fish.
But while the sight disturbed many residents, it was the stench from the water that drove most parkgoers away.
“We walk around the park every morning with our dogs,” said 14-year resident Kevin Drossel. “The smell had been there for many, many weeks. It was real strong. I’m surprised we couldn’t smell it from our house.”
Although park officials say they haven’t found a dead fish for about a week and the smell has begun to subside, the problem in Fountain Park, 12925 N. Saguaro Blvd., has left some residents, including Drossel, frustrated that conditions were allowed to get so bad.
“If they would just have someone take 20 minutes to walk around the park on a regular basis, I think they’d spot where some of these problems are,” Drossel said. “And they’d be able to get ahead of them, instead of waiting until they became so horrible.”
Park officials say conditions stemmed primarily from environmental conditions that could not be prevented. A warm July coupled with an exceptionally wet monsoon season turned the lake into an incubator for algae — a slimy peagreen organism with a rancid smell.
“We got so much algae bloom this year, the fish couldn’t keep up with it,” said Don Clark, Fountain Hills Parks and Recreation supervisor. “We treated it a couple of times this summer. But once the algae were killed, it kind of settled at the bottom of the lake and made the ammonia levels rise.”
Soon fish began to die and wash ashore.
“We were losing about 20 to 25 fish a day,” he said. “The buzzards came around for a few days and helped us clean up a bit.”
After that, not much could be done but let nature run its course, Clark said.
“We started running the fountain a little longer to help aerate the lake a little more,” he said. “But the cooler temperatures, which we are getting now, are what’s really helping to eliminate the conditions in the water.”
Man-made lakes, especially in urban settings, are often difficult to maintain and pose considerable challenges, said Eric Swanson, Arizona Game and Fish Department fisheries biologist.
Fountain Lake is primarily filled with reclaimed wastewater which contains high nutrient levels — one of the building blocks of algae.
Tempe Town Lake experienced a similar problem last month when excess algae caused elevated pH levels and made for unsafe swimming conditions.
“These lakes don’t have to be maintained as intensively as a swimming pool,” Swanson said. “But it does take regular, diligent attention to maintaining artificial lakes in these urban settings.”
To help prevent this from happening again, Fountain Hills is planning to upgrade the aeration system before next summer. “I think the parks department has done a very good job of addressing the problem,” Mayor Wally Nichols said. “We all did as best as we could to take care of the situation.”
• Algae are a major food source for fish and provide oxygen during the day.
• Limited amounts of algae are good for lakes, but too much can kill submerged plants and unbalance pH levels.
• As algae decompose, they create ammonia. Elevated ammonia levels kill fish.
• Algae have a distinctive smell. As they decompose they emit an odor resembling sewage.
Solving the problem
• Aerate. Park officials are extending run times for the fountain by 45 minutes to help aerate the water. The fountain will now run for 15 minutes at 8 a.m., 10 a.m. and 11 a.m.
• Wait. As the weather continues to cool, less ammonia will be created and that will improve conditions in the water.
• Improvements. By next summer the town plans to install a new lake aeration system.