Rock Lake



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Should we expand the Slow No Wake Shoreline Buffer?

As the number and types of Rock Lake users continue to grow, safety for all users can be improved by establishing a uniform Slow No Wake (SNW) buffer 200 feet from shore for all motorboats.  This will result in a very small increase of acreage reserved for Slow No Wake operation.  It will simplify the existing overlapping rules affecting swimmers, paddlers, and motor boaters, making the rules easier to understand and enforce.  It will also protect lake ecosystems and shorelines while improving Rock Lake’s aesthetics. The Rock Lake Improvement Association supports this change.

Where do we stand now?  
• 2/3/21:  Joint Rock Lake Committee (JRLC), a collaboration of Town and City of Lake Mills, recommended the Slow No Wake buffer expand from 100 to 200 feet.  At subsequent town meetings this committee and RLIA repeatedly requested action.  
•5/10/22: Town Board voted *not* to conduct a public hearing on the recommendation, effectively tabling it.  Their reported justification:  They did not have violation/enforcement information on Slow No Wake speed, they perceived wind causing more damage than motorized waves, they feared one change would lead to more requests such as a change in quiet hours and there were no indication of injuries within the SNW zone brought forward by WDNR.

To review, the current situation is complicated. According to Wisconsin DNR regulations, Rock Lake’s shoreline, and people who enjoy the lake, are protected by a 100-foot Slow No Wake buffer.  In other words, motorboats are required to maintain Slow No Wake speed within 100 feet of the shoreline as well as 100 feet from piers, rafts, and swimming buoys.  For personal watercraft (PWC or jetski) this distance is 200 feet. Finally, all motorboats must maintain Slow No Wake speed within 100 feet of swimmers, wherever swimming is allowed.

map of Rock Lake
Orange & red highlights show areas of Rock Lake affected by the 200 foot SNW speed proposal. A detailed explanation is in first FAQ below.

In addition, Sensitive Areas that are deemed Slow No Wake speed by Town of Lake Mills ordinance include:
• Schultz Bay (northwest side)
• Korth Bay (southwest side) 
• the Mill Pond 
• Marsh Lake (the basin of the lake south of the Glacial Drumlin Trail)

Expanding the Slow No Wake speed buffer to 200 feet from shore
• Establish the same buffer zone for both motorboats and PWCs.  This single regulation would be easier to understand and to enforce.
• Provide a safety buffer for swimmers and dogs, especially at Tyranena Park.
• Provide, in essence, a “Bike Lane” for distance swimmers and paddle sports enthusiasts.
• Move wake-producing motorboats farther from shore resulting in less disturbance to lake-bottom ecology and less shoreline erosion.

The impact of this change on lost acreage for unrestricted powerboating is estimated to be 24 acres, or less than 2.5% of the current unrestricted water surface.  Much of the shoreline not already protected by a Slow No Wake speed buffer is riparian shoreline with piers.  Motorboats currently should maintain Slow No Wake speeds 100 feet from the ends of those piers, or about 140 feet from the shoreline.  Therefore, a uniform 200-foot Slow No Wake ordinance would restrict less “open water” than one might think.

Why change now?
• The number of Rock Lake users continues to increase.  Many have called for improved safety measures to protect all types of watercraft, fishing boats, swimmers, even active use by dog owners.
• Overlapping statewide restrictions for personal watercraft (e.g., jet skis) already require SNW speed within 200 feet of shore.
• Special protections require SNW speeds near Sandy, Bartels & Ferry Beaches, and in Korth & Schultz Bays.
Limited expansion and simplification of SNW buffer responds to these concerns.  It would raise the protected portion of the lake from approximately 15% to 17% of the lake, the other 87% remaining unaffected.

Biggest safety concerns:
•Use of the lake has changed. There are more users of all kinds: increase in paddle sports; popularity of distance swimming
• More and faster pontoon boats with many towing
• Increased popularity of wake/surf boats which create large wakes that stir up lake bottoms and erode shorelines

Of particular concern:   Tyranena Park swimmers are allowed to swim 150 feet from shore yet power boats, at speed, are allowed to operate 100 feet from shore, unless the swimmers are easily seen.

Next Steps:  
• RLIA intends to meet with the the new Town of Lake Mills Police Chief once they are appointed, to encourage enforcement of existing SNW speed protections and understand water patrol priorities.
• Water Patrol will be invited to discuss this season’s safety issues during RLIA’s annual membership meeting on 8/27/22 at 10 AM, at Korth Park Pavilion.
• RLIA will consider enlisting citizen monitors to understand the scope of the problem.
• If you are concerned about this issue,  consider talking to your neighbors and posting information about it. Here is a recent letter to the newspapers.

Frequently Asked Questions:

 The Rock Lake Improvement Association calculates that the loss of open water would be minimal, less than 2.5%  of the lake’s acreage.  The impact of the changes are detailed here.

Slow No Wake Speed means a speed at which a vessel moves as slowly as possible while still maintaining steerage control.

Slow No Wake (SNW) benefits fall into two broad categories: Ecological (what’s good for the lake itself) and Recreational (what’s good for the community that is playing on/in the lake).  

Helps minimize conflict between various lake recreational users by creating a buffer from high-speed motorized users.  This buffer helps improve safety for the multiple users of the lake. Over the last five years, Rock Lake is seeing an increase in the number of paddle sport users (kayaks, canoes, stand up paddleboarders), open swimming, tubing and wakeboard boats, while water skiing and sailing have lessened.  Fishing is a constant.
A standardized SNW zone is easier to understand for recreational users rather than the current patchwork of zones.  The current policy is often cited by residents as most commonly violated.  These concerns were brought up in public comments and a public survey for the Rock Lake Management Plan. They are often mentioned to the patrol officers when those officers speak to community groups.  
-A larger SNW buffer can also reduce the noise level experienced by people on shore, or the passive users, which are the largest users of the lake.

-The major concern that SNW seeks to address is turbidity or the lake sediment getting kicked up and mixed into the water, especially in shallower water near shorelines.  When this happens, phosphorous that is bound in that sediment is released and can encourage algae blooms. The turbidity scours the gills of fish, interferes with fish who are sight hunters and also interferes with fish spawning. 
-Finally, waves reaching the shore contribute to shoreline erosion.
For more information on the ecological concerns, view the video in the last FAQ, below.

Absolutely.  According to the Clean Boat, Clean Water boat inspectors on Rock Lake, 36% of motorboats coming into Rock Lake were recently boating on a lake with 200 foot SNW rules.  These lakes include: Lake Ripley, Kegonsa, Waubesa, Monona, Mendota, and Lake Geneva.

This depends on a shoreline’s direct exposure to wind and the distance waves travel to reach the shoreline (known as its “fetch”).  Longer fetch and higher wind speed lead to larger waves.  Rock Lake shorelines generally have mild to moderate fetch.  Notably:

  • Research in Maryland (Zabawa and Ostrom, 1980) determined recreational boats cause significant erosion concerns for shorelines, particularly when operating closer than 200 feet at wake-producing speeds.  
  • Recent study of North Lake in Waukesha (Terra Vigilis Corp & Carrol University, 2021) used aerial and underwater drones to study wave impacts.  See a summary of their work here. They found:
    • Personal watercraft generated the least wave height and had no bottom impact.
    • Pontoon boats had longer wave lengths and minimal bottom impact.
    • Wake enhancing boats generated highest wave heights, longest wave duration and caused significant “bottom-scouring” and sub-surface impact.

Actually, adopting a 200 foot SNW buffer isn’t a ‘new’ idea.  In fact, Lake Ripley was an early adopter of a 200 foot SNW ordinance back in 1990.  At that time, jet skis were the fastest growing sector of the marine recreation industry.  Ripley updated their ordinance again in 2006.  This year, Lianna Spencer, their Lake Manager, stated that: “It (SNW) is currently (and has always been) perceived as an advantage to Lake Ripley; it helps prevent shoreline erosion and our residents view it as a good safety measure.”  Since 2000, motorized boats have gotten faster and larger.   In 2014, Dane county enacted  a 200-foot SNW on Lake Mendota, Monona, Waubesa, and Kegonsa.  Lake Geneva followed suit in 2017.

Currently, no.  Wakeboard boats are considered motorboats and subject to the same rules.  However, wakeboard boats create a larger wake which has an increased impact on shorelines and aquatic life in water less than 15 feet deep.  These impacts are being studied in other Wisconsin Lakes.  Here is a link to a contour map showing Rock Lake water depths.
For more information on the impact of wakeboard boats, view the video in the last FAQ, below.

Yes. This video presentation details a very interesting study of “enhanced” wave impacts on water quality and sediment re-deposition in a medium-sized freshwater lake in SE Wisconsin. It was created by Capt. Tim Tyre, PhD, USN(ret), Terra Vigilis Security Group & Prof. Mike Mortensen, Carroll University
Wave Propagation and Water Quality Impacts on Fresh Water Lakes

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