Dissolved oxygen (DO) levels within a body of water remain the great unknown to anglers, perhaps the last major mystery relative to fish location, winter panfish notwithstanding. Oxygen, of course, is as basic to life in water as on land. It’s an important indicator of a lake’s ability to support aquatic life. Levels above 5 parts per million are considered suitable to good for most fish, while few species survive for long at levels below 3 parts per million.

As important as DO is to aquatic life, we still know little about its persistence from lake to lake, or even between varying lake zones. Eventually, DO meters may become more widely available to serious fishermen. Today, most accurate DO meters remain too costly, as well as technically difficult to operate.

Some anglers have long questioned the theory of panfish and green weeds, as we’ve often observed and caught panfish mingling within forests of decaying plants. One point rarely addressed is that adequate oxygen levels often permeate vegetated littoral zones even throughout the last vestiges of prolonged North country winters. Data collected over a multiyear period by the University of Minnesota continue to demonstrate this. Consider a few facts:

• Mid-ice: January 20, 2000—Halsteds Bay, a hypereutrophic (highly fertile) basin of Lake Minnetonka, MN: 13 to 10 parts per million (ppm) DO from ice level to nearly 16 feet.

• Mid-to-late ice: February 25, 2000—Halsteds Bay: 7 ppm DO from ice level to 13 feet.

• Last-ice (just days before ice out): March 24, 1999—Ice Lake, MN (mesotrophic): 8 ppm DO from ice level to 23 feet.

• Mid-ice: January 16, 2002—Ice Lake, MN: 14 to 10 ppm DO from ice level to 24 feet.

• Late-ice: February 25, 2000—Lake Independence, MN (urban late mesotrophic): 6 to 8 ppm DO from ice level to 19 feet.

“Water on the Web” is an educational program instituted by the University of Minnesota-Duluth. The program teaches about lake and stream water quality through real-time data obtained from the project’s Remote Underwater Sampling Stations (RUSS units).

The website (waterontheweb.org) provides water quality information, much of which helps anglers better understand the waters they fish.