although containing sedimentary rocks, have 

 proportionally much more igneous material 

 (Keller and Reiser, 1959). The Alaska Penin- 

 sula is an area of current and historical volcan- 

 ism, and drainages of the Peninsula Systems 

 (including the Karluk) contain many deposits 

 of volcanic ash. 



The differences in seasonal changes of water 

 level and turbidity in the lakes are also' partly 

 due to differences in geology. Water levels are 

 lowest in the winter in all the systems. Because 

 lakes of systems tributary to Nushagak Bay and 

 those of the Chignik and Karluk systems receive 

 most of their water from snowmelt and rainfall, 

 water levels are highest during spring thaw and 

 autumn rainy periods. In contrast, lakes of the 

 other Peninsula Systems and of the Kvichak 

 system are low in the spring and tend to rise 

 during the summer because of melting ice fields 

 and glaciers. Turbidity often varies widely 

 among the lakes within a system because of the 

 localized source of rock flour carried by glacial 

 meltwater. Turbidity is highest during the sum- 

 mer, especially in lakes that receive glacial melt. 



The sockeye salmon lakes in southwestern 

 Alaska differ considerably in the length of their 

 ice-free periods, and presumably the growing 

 season also differs. In general, the lakes of the 

 Mainland Systems that are farther from the in- 

 fluence of the oceanic climate have shorter ice- 

 free periods than lakes nearer the coast. For in- 

 stance, the lakes of the Nuyakuk system are 

 farthest from the coast and are the last to be- 

 come ice-free in the spring. The upper lakes of 

 the Wood system do not usually become ice-free 

 until after June 1, whereas Lake Aleknagik, the 

 lowest lake in the Wood system, is usually free 

 of ice during late IVTay. In the Kvichak system, 

 Iliamna Lake, because of its large size and 

 greater exposure to ocean storms, loses its ice 

 cover earlier and forms it later than Lake Clark. 

 Breakup generally occurs by mid-May in Iliam- 

 na Lake, which occasionally has areas free of 

 ice during mild weather in the winter. 



Lakes of the Peninsula Systems, which are 

 more influenced by the oceanic climate and gen- 

 erally more exposed to wind action, may be ice- 

 free over long periods during the winter. The 

 ice in the Naknek system generally breaks up 

 in early May. Iliuk Arm seldom freezes over 

 completely, and the other Naknek lakes fre- 

 quently develop areas of open water during mild 



winters. Lakes of the Egegik and Ugashik sys- 

 tems, which are farther down the peninsula, 

 freeze later (if at all) than the Naknek lakes, 

 and the ice (if any) breaks up earlier. In the 

 Chignik system the shallower lake. Black Lake, 

 is free of ice sooner in the spring than Chignik 

 Lake. Both lakes are generally open by early 

 May and frequently develop areas of open water 

 in the winter. The Karluk system is strongly 

 influenced by the oceanic climate ; the ice in Kar- 

 luk Lake frequently begins to break up in April. 

 The lake occasionally remains ice-free during 

 mild winters. 



The two lakes in the Igushik system, Amanka 

 and Ualik, have similar areas, maximum and 

 mean depths, and volumes but have different 

 shoreline developments. Lake Amanka has two 

 distinct basins, which are separated by a sill, 

 but Ualik Lake has a single basin. The Kathlene 

 River flows from Ualik Lake into Amanka Lake 

 and enters the latter in its outlet basin. 



Lake Nunavaugaluk, the single lake in the 

 Snake system, is relatively deep and has only 

 one basin and a relatively low shoreline devel- 

 opment. 



The four main lakes of the Wood system (ex- 

 cluding Little Togiak) are similar in average 

 depth and shoreline development (if Lake Nerka 

 is considered to be two separate lakes joined at 

 their west ends). The deep end of each lake is 

 to the west among the mountains, and the shal- 

 lower east end extends into lowlands. All of the 

 lakes have altitudes of less than 50 m. (table 1) . 



The lakes of the Nuyakuk system contrast in 

 size and form. Tikchik Lake is relatively shal- 

 low. Lakes Chauekuktuli and Nuyakuk are 

 larger and extremely deep — each has a mean 

 depth of about 112 m. and a cryptodepression 

 that exceeds 170 m. 



The two major lakes of the Kvichak system 

 are sharply dissimilar in size and other morpho- 

 metric characters. Iliamna Lake is the largest 

 body of fresh water in Alaska. Its east end lies 

 among the mountains and has a deeply scoured 

 basin with an irregular shoreline, and because 

 of the many islands and bays, it has a high shore- 

 line development value. The western two-thirds 

 of the lake is relatively shallow and uniform in 

 depth and has few islands and a low shoreline 

 development. Lake Clark, much the smaller of 

 the two major lakes of the system, empties into 

 Iliamna Lake through the Newhalen River. It 



410 



U.S. FISH AND WILDLIFE SERVICE 



