Oil in Water
Potential contributors to oil pollution are all agencies engaged in deleterious effects of oily substances on domestic water supplies may be grouped into the following categories:
(1) hazards to health of consumers,
(2) the production of tastes and odors,
(3) the presence of turbidity, films or iridescence, and
(4) the increased difficulty of water treatment.
The taste and odor factor will control the threshold or limiting concentration of oily material acceptable in a domestic water supply. Many oily substances are harmful to fresh water aquatic life in the following manners.
Free oil and emulsions may act on the epithelial surfaces of fish. In other words, they adhere to the gills and interfere with respiration. Free oil and emulsions may coat and destroy algae and other plankton thereby removing a source of fish food. The coated organisms may agglomerate with suspended solids and settle to the bottom of the stream. Settlable oily substances may coat the bottom of the stream, destroy benthic organisms and interfere with spawning areas.
Soluble and emulsified material ingested by fish taint the flavor of the flesh. Organic materials may deoxygenate the water sufficiently to kill the fish. Heavy coatings of free oil on the surface may interfere with the natural processes of re-aeration and photosynthesis. Water soluble principles may exert a direct toxic action on fish or fish food organisms. Such toxicity may be acute or chronic.
Petroleum oils are also extensively used as solvents or vehicles for pesticides. While the oil may not in itself be toxic, it frequently increases the toxicity of the pesticide.
So far as they do not feed on each other they must be able to catch what flows by. They may have as parts of their bodies filter fans or they may spin nets to spread against the current, such as done by the caddis larvae. Others may have scraping devices such as snails or may fly nymphs, but in general they are usually predators and detritus feeders.
Among the fish that are normally encountered in swift streams are trout darters, black nose dace, and some suckers. Some of the warmer water fish, minnows, sun fish, bass, carp and catfish, are also inhabitants of rivers or streams.
Streams that empty into the ocean may have a special fauna of anadermous (upstream) fish
such as salmon, chad, stripped bass and some trout. These fish spend much of their life in the sea, but migrate into fresh water streams to spawn.