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<br />50 CHANGE
<br />I river. The trout are now gone from the lake and the suckers are endangered. Similar
<br />f reduction in flows of inlet streams during periods when they are used for spawning has
<br />apparently been at least partially responsible for the decline of the Clear Lake splittail
<br />in Clear Lake, Lake County (Cook, Moore, and Connors, 1966). Reduced stream flows
<br />~ ~ have, also altered the nature of the Sacramento-San Joaquin Delta and its fish fauna.
<br />Present flows are about half the natural level and by 1990 they will probably be
<br />reduced to about a third the natural level (Skinner, 1972). Besides reducing the
<br />aquatic- habitat, such diminished flows are likel to in r a
<br />y c e se the upstream penetration
<br />of salt water, decrease nutrient flow into the estuary, decrease the flushing action of
<br />the inflow and hence increase the effects of pollution, increase water temperatures,
<br />and decrease oxygen levels during the summer months. Such changes, unless controlled
<br />or mitigated in some way, are bound to have a deleterious effect on fishes of the Delta,
<br />particularly striped bass, Chinook salmon, white sturgeon, and American shad
<br />x (Skinner, 1972).
<br />i The ultimate reduction in fish habitat in California through dewatering has been the
<br />draining of lakes Tulare and Buena Vista on the floor of the San Joaquin Valley. They
<br />supported a small commercial fishery for turtles and native minnows in the nineteenth
<br />century. Unfortunately, the lakes were drained for farmland before anyone was able to
<br />take a look at the fish fauna but they probably were a major habitat for Sacramento
<br />perch, the now presumably extinct thicktail chub, and other depleted native fishes.
<br />One of the sad realities of California is that water which is not used directly for one
<br />purpose or another is likely to be polluted to a greater or lesser degree. Pollution is
<br />~, especially hard on the native fishes. In the foothills of the San Joaquin Valley, most
<br />native fishes are able to live only in clear, undisturbed sections of stream. The
<br />exception is the California roach, which ran be found in large numbers living in
<br />streams badly polluted with the effluent from small-town sewage-disposal systems.
<br />Fish kills from various types of pollution are common. In 1971, the fishes inhabiting
<br />the lower Pajaro River, including a run of steelhead, were virtually wiped out by the
<br />. failure of the sewage treatment plant at Watsonville, which released large amounts of
<br />raw sewage into the river. Three years earlier, a simIlar kill took place in the Pajaro
<br />{ when a farmer washed out his crop-spraying gear in the river, releasing highly toxic
<br />pesticides (Lollock, 1968). Bury (1972) recorded a kill of over 2,500 Pacific lampreys,
<br />rainbow trout, Klamath smallscale suckers, and speckled dace in a small stream in
<br />Trinity County, due to a spill of 2,000 gallons of diesel oil. A kill of several hundred
<br />rainbow trout in Mill Creek, Mendocino County, occurred in August 1973, when an
<br />airplane carrying a load of fire-retardent chemicals and clay accidentally dumped the
<br />x load into the stream rather than on a small wildfire burning nearby (H. W. Li, pers.
<br />comm.). Fish kills such as these, from a variety of causes, are not isolated incidents but
<br />are common occurrences that can, if repeated in one stream system, permanently alter
<br />the nature of its fish fauna.
<br />Although duect fish kills by pollution are common, equally significant to fish
<br />populations are nonlethal forms of pollution that decrease growth, inhibit reproduc-
<br />tion, or prevent migration. Laboratory studies of persistent pesticides, such as DDT,
<br />have shown that low levels can have such effects on salmon and trout, but the subtle
<br />nature of the effects usually renders it difficult to pin the decline of a fish population
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