What are the buoys floating in Moore Lake for?

Dave Lindquist, Fridley parks division supervisor, explained in an email:

The buoys in Moore Lake have thin ice signs mounted on them and are delineating the area where the lake ice typically remains open because of the aeration system that is used to add oxygen to the lake water to help with water quality. The buoys freeze in place and are a warning to people who might venture out onto the winter ice that there is open water. We came up with the idea of the floats about 10 years ago. It’s a much safer way of putting out the thin ice signs.

Editors' note: The leaves haven't jumped back on the trees. These photos were taken a few weeks ago.