TRAVERSE CITY, Mich. (AP) — The U.S. Coast Guard has begun its annual mission to remove buoys and beacons from the Great Lakes and the St. Lawrence Seaway before winter.

Crews with the Coast Guard’s Cleveland-based 9th District plan to retrieve 1,233 navigational aids by Dec. 28.

They are taken out of service during the icy season and replaced with buoys that are smaller, lighter and better able to stay afloat. They’re designed to ride underneath thick ice but stay on location.

The aids are part of a system that supports maritime traffic by marking safe passage for commercial and recreational vessels.

The system helps mariners find navigable channels, keep track of where they are and avoid danger. Officials say it’s similar to road signs and stoplights for automobiles.