discharges, from treatment plants that
skimp on chlorination of their effluent, or from storm runoff and
natural drainage off the land and urban pavements. But before anyone can
confidently say how dangerous it is to swimmers and others who make
intimate use of rivers and creeks, water scientists are going to have to
learn more about its measurement and classification than they presently
know.

[Illustration]

No easily applied method of testing can effectively establish the
guaranteed absence of human disease germs. The traditional "Coliform
Count" plays safe, as it must. It measures the concentration of certain
easily spotted "indicator" organisms that do not themselves make people
sick but are always voluminously present in the fecal discharges that
can carry harmful germs, and it gauges the danger by the concentration
of these indicators.

However, concentrations of coliform bacteria, originating in animal
manure or elsewhere, may invade a stream through runoff from rural lands
without having any meaningful relationship to human disease germs.
Counting them under such circumstances is a little like measuring the
depth of the proverbial well by the length of the pump handle.
Furthermore, no one really knows how easy or how hard it may be to catch
given diseases by swimming. In this country, outbreaks of leptospirosis,
an illness common to man and certain animals, have been traced to
swimming holes, and other links are obvious. On the other hand, some
careful British investigations turned up a good many quite healthy
people who habitually splashed about in sea water teeming with
pathogenic organisms of one sort or another. Sea water and fresh water
have vastly different qualities, but the subject is presently full of
confusion, and it needs much research.

Land runoff in general furnishes a large amount of pollution of all
classes, and in all parts of the upper Basin except the least-used
forest sections. Besides bacteria, heavy loads of organic material may
be washed into streams in regions with high densities of livestock or
poultry, and some pollution of this sort is found practically
everywhere. The wild and domestic animal population of the Basin above
Washington has been estimated to produce wastes equivalent to those of
about 3.5 million people. Much of this is dealt with by the "living
filter" of the soil, but much also reaches the streams, associated with
sediment from erosion producing rains. And the so