Town staff and council have been made aware of the Sunday morning event where Fountain Lake experienced a natural phenomenon known as a “fish kill.” This term refers to a localized die-off of fish population which is generally caused by reduced oxygen in the water. While unsightly, it is a part of the ecosystem of all bodies of water. The town has issued a release addressing some of the common questions surrounding this phenomenon.

What is going on? Ecological hypoxia (oxygen depletion) is one of the most common natural causes of fish kills. This may be due to factors such as algae blooms, droughts and high temperatures. Oxygen levels normally fluctuate, even over the course of a day, and are affected by weather, temperature, the amount of sunlight available and the amount of living and dead plant and animal matter in the water.

Why did this happen in Fountain Lake? This is a natural phenomenon that happens throughout the world, in both manmade and natural bodies of water. Fountain Park has had similar previous events, including an occurrence in 2006.

Over the past several weeks, much of Arizona saw extreme high temperatures from 104 to 109 degrees. These temperatures are not uncommon for the month of June. However, on Saturday, temperatures dropped drastically, reaching a high of only 81 degrees, and a much needed seasonal rain fell for most of the morning.

These elements are two likely causes of the situation in Fountain Park, as a fish kill can occur with rapid fluctuations in temperature or sustained high temperatures. Generally, cooler water has the potential to hold more oxygen, so a period of sustained high temperatures can lead to decreased dissolved oxygen in a body of water. Along with this, fish kills can also happen when there are dramatic changes in air and water temperature.

Additionally, Fountain Lake is naturally oxygenated through the process of photosynthesis. Plant life within the lake uses the sunlight to produce oxygen within the water. Saturday’s cloudy conditions prevented this natural process from occurring, which was an additional contributing factor to the situation.

How did fish get into Fountain Lake? The lake has been stocked with several types of fish intended to help with algae control. These include White Amur, or grass carp, which are herbivores that offer natural assistance to biological control. The fish kill that occurred primarily affected the Shad population, which are small feeder fish used to help with the filtering process and can often be seen just below the water surface in early morning and evening times.

Fountain Lake, which is manmade and fed with reclaimed water, does support marine life including algae, plankton, fish, turtles, frogs and others. The local lake is a haven for other wildlife including migratory birds and birds of prey that use the water as a hunting ground. Herons, egrets, ducks, swallows and other birds are regular visitors to the lake.

Can this be prevented? In small bodies of water, like Fountain Lake, mechanical aeration and/or removal of decaying matter (such as fallen leaves or dead algae) are practical preventive measures. Fountain Lake features 12 water movers and 32 water diffusers for just this reason. However, there is no way to completely eradicate fish kills.