The 200-Foot Lap

A wake boat running ballasted pushes much more energy downward than a ski boat does. In shallow water that energy reaches the bottom and stirs up sediment along with the phosphorus held in it, which feeds the algae blooms Winona deals with each summer. Depth keeps the energy off the bottom.

The Water Sports Industry Association runs the Wake Responsibly campaign, built on three points: stay 200 feet from shore and docks, keep music at a reasonable level, and avoid repeated passes over the same stretch. It gives no depth figure. The depth numbers in circulation, usually 10 to 15 feet, come from boat dealers and lake associations.

The shaded area on the map uses 20 feet, which is more conservative than any of those numbers. It is a local judgment call rather than a published standard.

I took Winona's shoreline from OpenStreetMap, projected it into meters, and laid it on a 4 meter grid. A distance transform then gives every point on the lake its distance to the nearest shore, and the 200 foot contour of that field is the loop on the map.

This has two useful effects. Inlets narrower than 400 feet close off, because no point inside them sits 200 feet from shore, which is right: there is no legal above-idle water in them. The loop also rounds the outside of each point and bay instead of tracing every wiggle, so it follows a line you could steer.

As a check, the same grid puts Winona's surface area at 569 acres, within about 1% of the published figure.

The deep water comes from the Indiana DNR's bathymetric survey of Winona from August 2017, a georeferenced map with contours every 10 feet. I read the 20 foot contour out of the file itself instead of tracing it by eye, then checked it against the OpenStreetMap shoreline. The survey's own lake outline lands within a few feet of it. I simplified the line to roughly a 40 foot tolerance for drawing.