BRAINERD, Minn. (AP) -- A University of Minnesota study links the decline of walleye in Mille Lacs Lake to a loss of habitat resulting from clearer water.

The study was published in the journal Ecosphere. Lead author Gretchen Hansen says researchers used 30 years of data on the lake's water clarity and temperature to estimate how walleye habitat has changed.

Walleye prefer low light and cooler water. But in recent decades, Mille Lacs' water clarity has increased, most likely due to septic system improvements around the lake and the invasion of zebra mussels. Hansen says that has reduced walleye habitat.

The study suggests that altering annual harvest levels based on changing water clarity and temperature could help sustain the walleye population. State officials currently base limits on the estimated number of fish in the lake.