Ken Bradbury (left) and Bob Nauta (right) at Big Spring in Fitchburg.

The GAC group looks into the spring-fed retention pond for the fish hatchery.

The GAC group at Big Spring. The light sandy areas underwater show where the springs well up to the surface.

A closer view of three spots where water is coming to the surface at different flow rates.

The group explores Nursery Spring, a larger spring than Big Spring with a flow of about one cubic foot per second.

Bob Nauta (center in blue) discusses features of Nursery Spring.

A closeup of the flow out of Nursery Spring.