The Winona Lake depth map, explained

In August 2017 the Indiana Department of Natural Resources surveyed the bottom of Winona Lake with sonar and published the result as a one-page bathymetric map. The title block records the essentials: Winona Lake, Kosciusko County, 562 acres, surveyed August 3, 2017, contours every 10 feet. The deepest labeled point reads 79 feet. The sheet carries the logo of BioBase by C-MAP, the sonar mapping system behind the contours, and it prints the DNR’s own reprint terms: “(Permission is granted to reprint with credit given to IDNR).” That permission line is the reason this site could trace every contour onto an interactive depth map, and it means you are free to print the PDF and keep a copy on the boat.

This article is a reader’s guide to that survey: how a 10-foot contour map works, what the bands reveal about the shape of the basin, why the acreage printed on the map disagrees with two other reliable figures, and how much of the lake holds water 20 feet deep or better.

How a 10-foot contour map works

A bathymetric map is a topographic map of the lake bed. Each line connects points of equal depth, and on this survey the lines fall every 10 feet: 10, 20, 30, on down to 70, plus a labeled point at the 79-foot maximum. The lines nest, so the map reads as a set of bands. Cross the 20-foot line heading toward the middle of the lake and everything beneath you is at least 20 feet deep until you cross the 30-foot line, where the floor of the guarantee drops another 10 feet.

Two cautions keep that reading honest. A band tells you the minimum depth of the water inside it, not the exact depth at any spot; a point just inside the 20-foot line might sit over 29 feet of water. And the contours record the lake as it stood on the survey date. Lake level rises and falls with rain and season, so the shape below you is stable while the exact number under your hull moves with the water on top of it.

One more wrinkle: not every ring on the survey means deeper water. Three rings enclose shoals, places where the bottom climbs back up through a contour instead of dropping through it. They carry no depth label on the DNR sheet, and the tour below points them out.

A tour of the basin

Spread the PDF out, or open the interactive version, and the lake resolves into four distinct pieces.

The main basin and the 79-foot hole

The deep water sits in one central basin. From most of the shoreline the bottom steps down band by band until it reaches the 79-foot hole near the middle of the lake, the deepest point the survey found. The Lilly Center for Lakes & Streams lists the lake’s average depth at 30 feet, a figure the DNR map itself does not print, and the contours make the pairing plausible: one deep central bowl, with the rest of the lake spread across the shallower bands around it.

The east shore drop-off

The east side falls away fastest. Along parts of the east shore the 20-foot contour comes within about 110 feet of the bank, which places genuinely deep water inside the 200-foot idle-speed zone that Indiana law (IC 14-15-3-17) draws around the shoreline. Depth and speed are separate questions there: the bottom drops fast, and the law still holds boats to idle within the 200-foot line. The boating map draws both lines so you can see exactly where they overlap.

The northwest arm by the canals

The northwest arm, the lobe that reaches toward the canals, is the shallow exception. Most of it is under 10 feet deep, with one small pocket that passes 20. On the map it reads as a broad pale shelf next to the dark stack of the main basin, and it behaves differently on the water too: in depths like these, wake energy reaches the bottom and stirs sediment, along with the phosphorus bound to it.

The mid-lake shoals

South of the deep basin the bottom rises from more than 20 feet of water to less than 10, then drops away again. This is the largest of the survey’s unlabeled rings, and a second, smaller shoal sits just east of it. Both rise well away from shore, in water that otherwise runs 15 to 25 feet deep, which is exactly where a boater has stopped expecting shallow water. The interactive map fills each shoal with the lighter color of its shallow side so they stand out from the deep bands around them.

Why three good sources list three acreages

Ask how big Winona Lake is and the answer depends on which careful source you consult. The DNR map’s title block prints 562 acres. The Lilly Center’s lake profile lists 571. The GIS work behind this site’s boating map, which traced the shoreline to compute the 200-foot idle line, comes out near 569. The spread is under 2 percent, and none of the three is a mistake.

Surface acreage depends on decisions that reasonable measurers make differently. Which shoreline dataset do you trace, and from what date? Where does the lake end and a channel begin: do the canals count, and the mouths of the inlets? A sonar survey, a printed profile, and a GIS tracing each answer those questions in their own way, and they measure at different moments besides, on a shoreline that moves whenever the lake level does. Small boundary decisions add up to a handful of acres on a lake this size.

The practical rule: say “about 570 acres” in conversation, and cite a specific source when precision matters. A permit application or a per-acre cost estimate should name the figure it uses and where that figure came from.

How much of the lake is deep water

By the boating map’s calculation, 319 acres of Winona sit at 20 feet or deeper, which is more than half the lake’s surface. The depth page extracted the same 20-foot contour from the same DNR survey by an independent route and computed 316 acres. The two figures differ by about 1 percent.

That small gap is useful in the same way the acreage spread is. Two separate readings of one source, made with different tools, landed within a percent of each other, which is a reasonable check that neither reading slipped. When you see 319 acres on the boating page and 316 on the depth page, you are looking at the same water counted twice; the difference is measurement noise.

Where to put the map to work

The survey PDF is the primary source, and three pages on this site each put it to a different use.

• The depth map: redraws every contour from the survey on an interactive map. Hover or tap a band for its depth; a dot marks the 79-foot hole, and the two shoals are filled in the color of their shallow side.
• The boating lap: overlays the 200-foot idle line, a 5.2-mile loop around the lake, on the deep water, so wake and ski traffic can see where legal speed and adequate depth coincide.
• For anglers: the contour steps on the south and east sides, and the edges of both shoals, are the structure where walleye, bass, and perch hold. The fishing guide covers the fishery and the regulations that apply.

The rest of the site’s maps, including the interactive watershed boundary, are collected on the maps page.

Before you go

The survey is a snapshot from August 3, 2017. A lake basin changes shape slowly, so the structure it records, the central bowl, the east-shore drop, the mid-lake shoals, and the shallow northwest arm, is still the best public picture of the bottom. The water level on any given day sits above or below where it stood that morning, and the shallow places are where the difference matters most. Treat the map as a guide to structure rather than a guarantee of clearance, keep the depth sounder on over the shoals and near shore, and slow down whenever the numbers start falling faster than the map led you to expect.