The high school students in Paul du Vair's aqua biology summer school course have learned to be extraordinarily game as they explore and record scientific data about Lake Mendota and its Six Mile Creek tributary. But there are a few things that make even these field-tested young ecologists shriek or howl out loud.

Like when they emerge from Lake Mendota or Six Mile Creek with blood-sucking leeches firmly attached to their legs. Or when they are hauling nets through waist-deep, murky water and big dark shapes bump against them. Or when they are wading along and suddenly step deep into a hidden, muck-filled hole.