MDNR info regarding fish kill and algae bloom

April Morey, Fisheries Management Biologist with MDNR- Fisheries Division provided the following information to the SLA regarding the current fish kill and algae bloom. Most notably in the final paragraph she states "For now, continue to avoid contact with water that appears green, has visible surface scum, or otherwise looks unusual. Clear water is safe water":

"I spoke with Brian Zuber, who is the lead for the Sanford Lake fish kill event and an Environmental Quality Analyst with EGLE. I was able to confirm that water samples were collected last week and again today from Sanford Lake by district staff. 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.

HABs can be a little confusing because, despite the name, they are actually caused by a bacteria called cyanobacteria, commonly referred to as blue-green algae. Cyanobacteria can photosynthesize and can rapidly multiply when environmental conditions are favorable (hot, stagnant, abundant organic matter, etc). Sometimes the cyanobacteria produce cyanotoxins, while other times it may just primarily contribute to fish mortality through changes in water quality, including oxygen depletion as the bloom grows and decomposes.

The recent refill of Sanford Lake likely created several conditions that could have contributed to the bloom. The reservoir had approximately six years of exposed bottomlands that were recently inundated. As terrestrial vegetation and other organic material became submerged, decomposition likely released nutrients into the water. Nutrients that had accumulated in the exposed bottomlands may also have been resuspended during the refill. These additional nutrients, particularly nitrogen and phosphorus, can provide fuel for cyanobacterial growth. Fertilizer applications and associated runoff from the watershed can further increase nutrient availability.

Another important consideration is the role that aquatic vegetation and filamentous algae may play as the reservoir ecosystem continues to re-establish following the refill. Healthy aquatic plant communities are an important part of a functioning lake ecosystem and can compete with cyanobacteria for nutrients and light. As Sanford continues to transition from exposed bottomlands back to an aquatic ecosystem, the development and distribution of aquatic vegetation and filamentous algae will be an important component of that process - this is why PLM is limiting treatment of native plants and algae right now. A well-established plant community can help retain nutrients within the system, provide competition for available resources, and provide important habitat for fish and other aquatic organisms.

The hot summer weather may also be contributing to the fish mortality. Warm water naturally holds less dissolved oxygen than cold water, and oxygen can be consumed rapidly when large amounts of organic material are decomposing. This can result in naturally occurring low dissolved oxygen conditions, which can stress or kill fish. Given the recent refill, all of these things are likely happening and interacting with one another. 

Unfortunately, there is not a silver bullet for dissipating a HAB once it has developed. Depending on the species and environmental conditions, HABs can dissipate very quickly or persist for several weeks. The best (and really only) approach is to allow the bloom to run its course while we continue to monitor conditions.

For now, continue to avoid contact with water that appears green, has visible surface scum, or otherwise looks unusual. Clear water is safe water. I will continue to follow the sampling results and provide additional information as it becomes available."

The SLA will continue to share (via website and Facebook) information as it is provided to us.