WHAT IS A SNAGBOAT?

The W.T. Preston on dry ground.
I'm a Californian. We have rivers? I lived in upper Michigan on the lake. Many rivers flow to the lakes? I never heard of a snagboat.
The snagboat, W.T.Preston was put out of service in 1981 and has a long and colorful history of removing snags from the rivers that pour into Puget Sound. Snags? And, according to one captain, a local might have a cow stuck on a small bar at low tide. The snagboat would lift it off for him. Or, perhaps a tug would have a fish net, or a rope fouling his propeller. The snagboat would lift the tug up an allow the skipper to cut his propeller free. Just a little service to the locals. The crews were paid for 8 hour days, but were on call and worked whenever and wherever needed.
The W.T. Preston is one of only two snagboats left in the U.S. The interpretive center for this amazing boat was so well done, I could hardly wait to get on the boat and look around. I kind of wondered about snags, though.
The pictures below, (pictures of pictures) show the size of some of these snags. The interpretive center has a video showing the snagboat in action. It could pick up a 40 ton snag. The town of Anacortes competed to have the historical boat housed here and I'm so glad they did.