FOND DU LAC, Wis. (AP) _ Nets are placed along the shore of Long Lake to harvest fish for the sake of scientific data.

The nets capture northern pike, walleyes and largemouth bass from the popular fishing and recreation spot in the northern unit of the Kettle Moraine State Forest.

Once each day, a crew from the state Department of Natural Resources' office at Horicon wrestles fish-laden nets aboard a boat and empties the catch into tubs.

In a matter of minutes, a three-man team bends to the task of measuring fish, tagging them, recording information and releasing them.

The project at Long Lake, situated in the southeastern corner of Fond du Lac County, northwest of Milwaukee, could have implications for many Wisconsin lakes used by anglers.

James Congdon, DNR fish manager for a five-county area served by his Horicon office, says the fish-tagging project and year-long creel census are designed to learn more about the effects of fishing pressure.

''Hopefully, it will give us information that will help us manage the lake better,'' he said in a recent interview. ''It probably will have implications for other lakes in the state.''

Congdon concedes that the DNR is scrutinizing the idea of ''showcase lakes,'' but he says specific lakes - and that includes Long Lake - have not been designated.

The concept of showcase lakes is to demonstrate to the public what can be accomplished by concentrating efforts on a particular body of water or a specific problem. Congdon insists that showcasing doesn't mean the DNR will be dropping management of other lakes.

He says Long Lake was selected for the ongoing study because it boasts a naturally reproducing northern pike population and can be expected to generate plentiful statistics.

Congdon also points out that the DNR can rely on good cooperation and support from a local fishing club. Members of the Long Lake Fishing Club approached the DNR several years ago when they noticed the walleye population was declining.

The DNR responded with projects to boost the population and joined forces with property owners and the fishing club to build rock spawning reefs in the lake.

Long Lake historically has been a ''good fishing'' lake, Congdon says.

Located at the headwaters of the Milwaukee River, it is used not only by local fishing and outdoor enthusiasts, but also by an even larger group of travelers, campers and vacationers from southeastern Wisconsin.

Congdon is enlisting the help of anglers who use Long Lake in the hope of developing a viable project.

Since ice has disappeared from Long Lake, DNR personnel have tagged almost 500 northern pike, more than 150 walleyes and more than 150 largemouth bass. If time and conditions permit, they will tag 3,000 to 4,000 blue gills as well.

Dennis Michael, a 22-year DNR veteran who is working on the project, says they will continue netting and tagging until the number of fish trapped diminishes significantly.

''We'll be doing some boom-shocking here in May'' in the hope of adding a larger number of bass to the tagging sample, he said.

Michael says the largemouth bass population appears to be in very good shape. Nets have yielded a broad range of bass, with many in a class that would tempt most any bass angler.

The number of walleye, however, is not encouraging. Many fish in the 20- to 24-inch range have been tagged, but there have been few small fish - an indication of poor survival and lack of natural reproduction.

A reef project has shown signs of success, but there are some problems.

''One of the reefs is already covered with weeds and debris,'' Congdon said.

Walleyes need a good reef for natural reproduction, says Congdon.

''We're definitely going to stick with it and do what we can to improve the walleye population,'' he said.

Congdon says fishermen will be encouraged to return fishing tags to the DNR by mail or to any of several stations available around the lake.

That cooperation is crucial to the success of the project, Congdon says.

''We are hoping to get a lot of those tags back,'' he said.

The tagging operation will be followed by a year-long creel census.

''We expect to learn what effect the fisherman has on the fish population of a given lake,'' said Congdon, who expects a written report to be completed by the spring of 1988.

End Adv Weekend Editions April 26-27