Rock Lake Improvement Association

Lake Information

Rock Lake Clean Boats, Clean Waters - 2017 Effort & Results

Beach Water Quality Testing Results for Sandy Beach, Bartel's Beach, Tyranena Park, and Ferry Park can be found here:
If the E. coli in the water exceeds 235 cfu/100 ml, then an advisory sign is posted at the beach. If the E. coli in the water exceeds 1,000 cfu/100 ml, then a beach closure sign is posted. To find out more about beach water sampling, advisories, closures, and E. coli see: Beach Advisories, Clousures and Human Health

Harmful Algal Blooms in Wisconsin's Lakes...they may look like thick paint floating on the water and frequently give off a foul odor... Further information on Blue Green Algae blooms are at:

Swimmer's Itch; is neither dangerous nor contagious, but it is very uncomfortable.

Add a Shoreland Garden or Rain Garden to your Rock Lake property! Check the Healthy Lakes website ( and contact Patricia Cicero at the Jefferson County Land and Water Conservation Department for next steps and financial assistance (, 920-723-2728).

The latest report, includes Rock Lake
Aquatic Invasive Species - Jefferson County

City Drains that Flow Directly to our Lake (Map)

View Presentation Slides from Seminar:
Lake Systems, Algae, Plants, and Plant Management Laws

"Welcome to Rock Lake" area information with a map, created by the Joint Rock Lake Committee.

Map of the Rock Lake Watershed, see what a drop of rain flows through to get to the lake.

Aerial photo of Rock Lake, 1994, Robert T. McCoy Photography.

Aerial Winter Photo, Rock Lake 3/13 Stan Smoniewski

Korth Park - All about the history and ecosystems of this treasure that contains 1300 feet of shoreline, 89 total acres of land.

Bowfin Facts - why this native fish is good for the Lake.