Can walleyes make a lake clearer?

We all like our lakes to be clear, and most of us prize walleyes as a sport fish and table fare. But is there a connection between the two? Between walleyes and water clarity?

I learned at this year’s Wisconsin Lakes Partnership Convention that there can be. Scott Van Egeren, a water resources management specialist with the state Department of Natural Resources, gave a talk on the food chain in typical lakes such as we have in Wisconsin.

To oversimplify matters a bit for brevity, the food chain starts with one-celled algae (plant plankton, or phytoplankton), which are eaten by animal plankton (zooplankton), which include small crustaceans like Daphnia (water fleas). Fish such as cisco (planktivores) eat the algae eaters, and predatory fish, including walleyes, eat the cisco.

Now, what has that to do with water clarity? Well, in general, the lower the level of algae in a lake, the clearer the water. And in general, the more algae-eating water fleas are present, the less algae there will be. But what happens if cisco (and other smaller fish) are abundant and are gobbling up the water fleas? That means fewer algae-eaters, more algae, and cloudier water.

And here is where walleyes come in. Walleyes graze on cisco. If the walleyes are abundant, they can thin out the cisco and other smaller fish considerably. That means the water fleas and other algae-eaters have a chance to thrive, and the algae population goes down. And the water is clearer.

Now, of course, water clarity has to do with much more than just the walleye population. An important factor is the level of nutrients – which cause algae to thrive and can lead to nuisance blooms. Other factors include lake depth (deeper water has more capacity to absorb nutrients), surrounding land uses (which can contribute sediment in runoff), and wind and wave action, (which especially in shallow lakes can stir up sediments from the bottom).

But it’s interesting to think that a healthy population of walleyes can have a benefit beyond providing mornings and evenings of excellent fishing.