Water pollution is caused by various factors ranging from human activities
to natural factors.
However, it is estimated that domestic waste water from households accounts
for nearly 80% of all such pollution.
The water quality of rivers has improved due to the broad introduction
of sewage systems in urban rivers, though the rate of improvement has steadily
Meanwhile, Tokyo Bay and enclosed waters such as Lake Sagami have had red
tides and algae blooms due to eutrophication.
Due to rapid urbanization and high industrial activity, Kanagawa presently
faces problems with the drying of groundwater supplies and the contamination
by organic chlorides in many areas.
While ground subsidence is occurring in limited areas, ground subsidence
covering large areas has decreased.
The environmental impacts of residual hazardous substances in the soil
are matters of concern, since the environmental quality standards regarding
contamination of the soil have been exceeded in some areas.