If you’re ready to enjoy summer on the Great Lakes, you might be in for a very cold surprise.

After a cooler-than-normal May, water temperatures across the lakes are slightly below average for this time of year, according to the National Weather Service. While the difference is just a few degrees, it’s enough to make early-season dips feel extra chilly.

The lakes typically don’t hit their warmest temperatures until late August.

Bridge Michigan reports the average surface temperature in Lake Michigan is just over 45 degrees, with the warmest waters in the southern tip of the lake. Lake Superior is the slowest to warm up, while Lake Erie heats up the fastest.