One way of determining the life forms of a lake is by noting the food of the fish. During the last three weeks of July and the first week of August, fifty fish stomachs received from fisherman from the lake were examined and their contents noted. All but four of these fish were Silverside trout averaging sixteen and a half inches in length; the four were small Rainbow trout. In examining the contents of the stomachs one is impressed by the fact that the diet of a particular individual is apt to be of one kind of food rather than from a wide range of kinds. For example, one fish will have concentrated on snails, one on midges, one on water fleas, and one on water-stranded land insects, or perhaps on worms. The largest individual form found was a seven-inch fish; the smallest individual used for food (exclusive of forms such as diatoms which are basically food of the fish food) is the water flea of Daphnia pulex (fig. 1). This minute crustacean was found in 74 percent of the fish examined and made up 62.8 percent of volume of food eaten by the fifty trout. These forms are rarely found at the surface of the lake, being most abundant at depths of 75 to 200 feet. The closely related Amphipod (fig. 2) locally known as fresh-water shrimp which is fairly abundant in the marginal waters of the lake is sixth in importance as fish food; it was found in 24 percent of the stomachs and made up 4.7 percent of the volume of food used by the fifty fish.

In point of total bulk, the snails come second in importance as food, as they make up 10.9 percent of the food eaten. The snail used most by the fish is Pompholex species? (fig. 3) the middle-sized form of the three Crater Lake snails. It was found in 22 percent of the stomachs examined.

The various forms of insects make up the third largest amount of fish food, 9.6 percent, and were used by 54 percent of the fishes. However 6.86 of the 9.6 was made up of midges, larvae, pupae and adult stages (fig. 4). In some cases these made up the entire stomach contents. Land insects, when stranded by adverse wind currents sometimes make up the food; one fish had 11 beetles, 1 moth, 1 grasshopper or cricket, an ant, 1 bee, 2 bumble bees, 2 true bugs, as well as adult and pupa stages of midges, 3 snails and 1600 Daphnia. Of the water insects other than midges the Caddis fly, especially in the larva (penniwinkle stage) (fig. 5) is quite a favorite of off-shore feeding fish. They made up 1.66 percent of the volume of fish food though found in but 14 percent of the fish. Mayflies also form part of the fishes' diet (0.65 percent)

The annelids formed only 2.53 percent of the food mass. Three small leeches (38 inch) were noted, and one stomach was largely filled with 65 worms, smaller than the earthworm but closely allied to it. These worms have been found in muddy pools along the lake margin and also in bottom tows to a depth of 90 feet.

The two fishes found in the diet made up 8.7 percent of the total mass though found in only 4 percent of the fish stomachs. The distinguishable plant material was relatively small, being only 0.8 percent of the diet and consisted of leathery Nostoc, a blue-green algae (fig. 6) and wads of filamentous green algae, probably Zygnema (fig. 7).