Levels of cadmium, cyanide, and other
toxins (health-affecting substances) have
been dramatically reduced. At present,
there are few problems with these toxins.
However,thelevelsoforganic
contamination (substances affecting the
living environment) remain high. Efforts to
improve water quality in lakes, bays, inland
seas, and other closed bodies of water have
not been successful. Water circulation is
poor in these types of closed water systems,
and nitrogen, phosphorus, and other
nutrients can cause rapid proliferation of
algae. The progressive worsening of water
quality has led to eutrophication, which
causes red tides or blue tides and harms
local fish populations and other aquatic life
(See Figure 7.2).