The Incredible Myth about Illinois Lake Depth

In our experience as land brokers, no asset has drawn more attention and value than water…especially lakes.  We currently have around 2000 clients looking for land and I would guess half of them are looking for land with a lake on it.  However, our clients knowledge on lakes is surprisingly limited.  This blog is being written to help establish the importance, or lack there of, of lake depth.

“How deep is this lake?”, “Whats the average depth of this lake?”, etc… It is far and away the most common question when we show clients lakes.  My answer is usually to spit out the deepest part of the lake…which in Illinois can be anywhere from 8′ to 75′ depending on the lake.  However, what I really want to say 99% of the time is…”who cares?…it isn’t important.” And here is why…

When most of my clients are asking this, they believe that the deeper the water, the better the fishing is.  They believe that the pure amount of water increases the carrying capacity for fish. They believe that Illinois fish like the deeper water in certain times of the year.  Ultimately, they believe that deeper water produces and harvest more and better fish.  Here is the thing about that though…it is 100% wrong.

Sample Lake Depth Chart

Looking at native Illinois Fish

Largemouth Bass: ideal habitat is 0-12 feet.  For the most part, anything deeper than 12′ is wasted or unneeded depth.

Bluegill: Spend most of their time in less than 3′.  They will go up to 15′ in the spring and post spawn…but certainly dont need it.

Crappie: will build nests in 2-20 or so but spend almost all of their life in under 10′.  You will run into some deeper crappie in the hot summer days but in no way do they need any depth over 12 or so.

The common denominator here is weed depth.  In central Illinois, we most commonly see vegetation anywhere from 0-12′.  Thats where the fish can hide and feel safe. Thats where the baitfish live. You hear a lot of fish biologist refer to really deep water as dead water.  What they mean is that where there is no vegetation, the carrying capacity nosedives.  So in essence, often times you DONT want really deep water. There are definitely some advantages to deep water, which I will address shortly.  However, increased depth does not usually equate to more or better native sporting fishing in the midwest.  For example, comparing the following to lakes…

Lake A          10 Total Acres     5 Acres <12′          5 Acres >12′
Lake B           8 Total Acres      7 Acres <12′          1 Acres >12′

In those two scenarios, Lake B will most often hold more fish!

There are a few elements that do relate do depth…they are as follows.

1) Winter Freezes: Although I have seen lakes with 25’+ have winter kills, you are typically in the safe zone when over 20% of your lake is 8′ or greater.

2) Siltation: Not always, but sometimes, when you see depths under 18′, you have to question if the lake is silting in.  The most appropriate question to find out if siltation will be an issue is “How many sq acres of runoff feed this lake.  If it is more than 20 times the surface acres of the lake, it may be a concern…but those cases are rare.

There are also a few very specific benefits to deep water.  They are as follows…

1) Potential for northern US species to reproduce.  Species like smallmouth bass and walleye have an outside chance to reproduce when you start seeing depth in that 30’+ range.  It is pretty rare but we have seen it happen.  Walleye and smallmouth will live and thrive in lakes with averages depths in the 18-25 range but reproduction chances plummet…meaning you have to stock them more frequently.

2) Waterfowl: If you are a waterfowl hunter, deep lakes tend to stay open longer…extending your hunting season.  Additionally, if you install an aeration system…the deeper the diffuser, the more water that stays open.

This by no means is a comprehensive list of all the negatives and positives of water depth, but it certainly addresses the most common issues that we explain on a daily basis.  The bottom line is that somewhere along the line, water depth has come to be associated with bigger and more fish when that is not the case at all.  Water depth is an important thing to know…but it typically doesn’t have anything to do with the quality of the fishing.

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