Coliform bacteria are excellent microbiological indicators of the
concentration of pathogenic viruses and bacteria in water, and coliform
data are used to regulate the use of Bay waters for contact recreation
and shellfish harvesting. Although coliform bacteria are indigenous
to natural waters, human activities have increased their numbers from
both point and nonpoint sources of human and animal fecal material
and decomposing organic wastes. Marginally-treated and untreated sewage
and liquid wastes from industries such as dairies; food processing
plants such as canneries, frozen-food plants, and meat and shellfish
packing plants; and tanning, textile, and pulp-and-paper plants may
contribute large numbers of fecal coliforms to tidal waters. Nonpoint
source runoff washes large numbers of these microbes into the estuary
from their natural habitats in soil and on vegetation, but the major
nonpoint sources of coliform bacteria include wild and domestic animal
wastes, for example, from large concentrations of cattle, ducks, geese,
dogs, and cats; failing septic systems; and decomposing organic material.
Data in the Coliform data set is for study dates 1953-1981 and were
compiled by staff at the EPA Chesapeake Bay Program from the agencies
in Maryland and Virginia which regulate shellfish closures due to
coliform contamination.