7409

• UCREFRP Catalog Number: 7409
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1991.
• USFW - Doc Type: Progress Report No. 15,
• Copyright Material: NO

Summary

The Quality of Water, Colorado River Basin,
Progress Report is prepared and updated every
2 years to summarize the status of water quality
in the Colorado River Basin (Basin). Although
several water quality parameters are reviewed,
salinity is by far the most serious and is allotted
a major portion of this report.

The Colorado River provides municipal and
industrial water for more than 18 million people
in seven states and irrigation water to more
than 1. 7 million acres of land. The Colorado
River Basin reservoirs now have a combined
storage capacity of about 60 million acre-feet.
While water quality is generally adequate for
industries, wildlife and livestock watering, and
public water supplies, nutrient loading to the
main stem reservoirs is becoming a problem as
development and associated pollution increase.

Increases in phosphorus and nitrogen, elements
that are essential to the growth of algae, the
base of the food chain in reservoirs, are causing
some portions of the reservoirs to become
eutrophic (overly productive). Eutrophication of
reservoirs can impair municipal, industrial, and
recreational uses by causing taste and odor
problems, creating toxins, and reducing the
dissolved oxygen available for fish and other
aquatic organisms.

While nutrients are causing some reservoirs to
become eutrophic, reservoirs further down-
stream are becoming nutrient-poor due to the
trapping of nutrients in the upstream reservoirs.
This trapping of nutrients reduces the
productivity of the fisheries by limiting their
food supply. Studies are described in chapter 3
which help to define and resolve some of these
problems in the Colorado River Basin.

Another major concern in the Colorado River
Basin is the threat of salinity in both the United
States and the Republic of Mexico. Increases in
salinity are important in the Basin because of
the effect of salinity on crops and on municipal
and industrial users. High salinity increases
water treatment costs, damages plumbing and
fixtures, increases maintenance on pumps and

distribution systems, lowers crop yields, and
increases the need for special drainage facilities
on farms.

Historically, the Colorado River carries about
9 million tons of salt past Hoover Dam in
10 million acre-feet of water per year. The
salinity comes primarily from natural diffuse
sources, saline springs, and agricultural sources.
Natural sources add almost half the total salt
load, irrigation return flows add over one-third,
and municipal and industrial sources add the
remainder.

Several laws have been passed by Congress to
maintain the salinity at acceptable levels in the
United States and to meet our obligations with
Mexico. Public Laws 93-320 and 98-569
authorized the Secretaries of the Department of
the Interior and Department of Agriculture to
enhance and protect the quality of water
available in the Colorado River for use in the
United States and the Republic of Mexico.
Under Title I, a desalting plant, brine discharge
canal, and other features will enable the United
States to deliver water to Mexico having an
average salinity no greater than 115 parts per
million (ppm) +/- 30 ppm over the annual
average salinity of the Colorado River at
Imperial Dam.

The Act also authorized the Secretary of the
Interior to construct five salinity control units
and authorizes the Secretary of Agriculture to
implement an onfarm salinity program.
Further, the Secretary was directed to
undertake research on additional methods to
control salinity and to cooperate with the
Department of Agriculture and others.

In 1989, the average annual salinity level in the
Colorado River was within the standards, due in
part to the Interior and Agriculture salinity
control programs. These programs are removing
about 183,500 tons of salt annually from the
river system. The salinity at Imperial Dam is
projected to approach the numeric criterion level
of the salinity standard but not exceed it if
implementation of the salinity control program