Sanford Lake Fish Kill Update: What We Know

We have an important update regarding the recent fish mortality on Sanford Lake.

Sanford Lake Association spoke with April Morey, Fisheries Management Biologist with the Michigan Department of Natural Resources (MDNR). April spoke with Brian Zuber, Environmental Quality Analyst with EGLE and the lead for the Sanford Lake fish kill event.

Based on the information available so far, the signs continue to indicate that a harmful algal bloom (HAB) is likely responsible for the recent fish kill. Water samples were collected from Sanford Lake by district staff last week and again today, and monitoring is continuing.

What is a harmful algal bloom?

Despite the name, HABs are not caused by traditional algae. They are often caused by cyanobacteria, commonly called blue-green algae. Under favorable conditions—such as hot weather, stagnant water, and abundant nutrients—cyanobacteria can multiply rapidly.

Some cyanobacteria produce toxins, while others can contribute to fish mortality by changing water conditions, including depleting dissolved oxygen as the bloom develops and organic material decomposes.

Why could this be happening in Sanford Lake?

The recent refill of Sanford Lake has created a unique set of conditions.

For approximately six years, the lake bottom was exposed. When the reservoir refilled, vegetation and other organic material became submerged and began decomposing, which likely released nutrients into the water. Nutrients that accumulated in the exposed bottomlands may also have been resuspended during the refill.

These nutrients—particularly nitrogen and phosphorus—can provide fuel for cyanobacterial growth. Nutrients entering the lake through watershed runoff can contribute as well.

The lake's ecosystem is also still re-establishing itself following the refill. Aquatic plants and filamentous algae are an important part of that process. Healthy aquatic vegetation can compete with cyanobacteria for nutrients and light, help retain nutrients in the system, and provide important habitat for fish and other aquatic organisms.

This is one reason PLM is currently limiting treatment of native plants and algae while the lake's ecosystem continues to develop.

What role is the hot weather playing?

Warm water naturally holds less dissolved oxygen than cold water. At the same time, large amounts of decomposing organic material can consume oxygen rapidly.

The combination of warm temperatures, decomposition, nutrient availability, and a newly refilled reservoir may be creating conditions that are contributing to the fish mortality.

What happens next?

Unfortunately, there is no quick fix or "silver bullet" for a HAB once it develops. Depending on the species and environmental conditions, a bloom can dissipate quickly or persist for several weeks.

For now, the best and only approach is to allow the bloom to run its course while MDNR and EGLE continue monitoring conditions and evaluating the water samples.

⚠️ PLEASE AVOID CONTACT WITH UNUSUAL-LOOKING WATER

Until we know more, do not enter or come into contact with water that:

• Appears green• Has visible surface scum• Looks unusually cloudy, discolored, or otherwise abnormal

When in doubt, stay out.

We will continue to share information with the Sanford Lake community as it becomes available from MDNR and EGLE.

Thank you for your patience and cooperation as Sanford Lake's ecosystem continues to re-establish itself following the refill.