TRAVERSE CITY, Mich. (AP) — Free tours are available this fall at three northern Michigan sites where crews collect Great Lakes salmon as the big fish migrate up rivers.

The tours are offered at weirs on the Boardman River in Traverse City, the Little Manistee River in Manistee County and the Upper Platte River in Benzie County.

Weirs are structures that block upstream fish passage. Staffers with the state Department of Natural Resources gather chinook and coho salmon at the weirs. They used fertilized eggs from the captured fish to produce more salmon.

Tours deal with topics such as salmon biology, how weirs and fish ladders work, invasive species, state fish hatcheries, and the DNR's annual egg collection efforts.

Officials say each of the weirs has its own tour schedule.