Yes there are Rattlesnakes at Devil’s Lake. Specifically the Timber Rattlesnake. It is not often you will see one however. Timber rattlesnakes tend to shy away from areas where people are about. They are normally not aggressive and will crawl away when they sense your presence. On occasion hikers have encountered one along the trails and reported it to the park staff.
Timber rattlers are listed as a Protected Wild Animal in Wisconsin. This means it is illegal to take or kill this animal unless there is an immediate life-threatening situation involving a human or domestic animal life. There has only been two verified death in Wisconsin due to a rattlesnake bite since 1900 and only one bite is averaged every four years in the state. In the summer of 2000 a dog was bitten on the Steinke basin trail in Devil’s Lake State Park. If you were to be bitten by a rattlesnake in the park, notify authorities immediately and follow instructions. In most cases you can simply hike out, then drive to St. Clare Hospital in Baraboo.
More commonly you may see a northern water snake. You can recognize it by its grayish-brown color with a banded neck and alternating dark blotches on its back. The snake is not poisonous however it has an anticoagulant in its saliva that causes victims to bleed a lot when bitten. If you see this snake, back away and do not touch! It tends to be a little more aggressive if it feels cornered. The northern water snake is quite common to lakes, ponds, swamps, and other bodies of water throughout the Eastern United Sates. It can grow up to 53″. Normally this snake is encountered while it is basking on stumps and rocks or when it is hunting along the weed beds.
In total there are approximately 13 species of snakes in the park from the common but small red-bellied snake at only about a foot in length, to the Black Rat Snake which can get up to a daunting 5 ft in length*. However no snake in the park is poisonous other than the Timber Rattler.
Just remember to stay away from the snakes. They are doing their best to stay away from you.
*ref: Lange, Kenneth L. 1989. Ancient Rocks And Vanished Glaciers: Worzalla Publishing Company, Stevens Point, Wisconsin. (pg 72)