Document Type

Technical Report

Publication Date



The Nevada Division of Environmental Protection (DEP) has proposed water-quality standards, applicable to Las Vegas Bay and Lake Mead, for (1) chlorophyll, (2) un-ionized ammonia, and (3) pH.

We have concluded that the proposed standards are unlikely to protect or improve water quality in Lake Mead. The proposed chlorophyll standard:

May harm the fishery. Lakes with more chlorophyll have greater fish production.

Will not improve clarity. Chlorophyll concentrations above 30 ug/1 have little effect on clarity.

Will not protect against scums or dominance by blue-green algae. Lake Mead shows no consistent relationship between chlorophyll and scums or blue-green dominance.

Will not safeguard the drinking-water supply. Chlorophyll is irrelevant to the drinking-water supply.

The proposed standard for un-ionized ammonia depends on the assumption that a problem exists, but there is no evidence of any problem caused by un-ionized ammonia. If there is no problem, then the money spent "correcting" it will be wasted.

The proposed pH standard is unnecessary to protect any beneficial use. It is intended to prevent degradation of higher quality waters but, because of a statistical defect, it would be violated by random variations even if there were no degradation.

DEP expects to implement the proposed chlorophyll standard through restrictions on the municipal discharges of phosphorus. However, the wastewater-treatment plant operated by the Clark County Sanitation District and the City of Las Vegas have been removing phosphorus since 1981. Although $170 million has been spent on phosphorus removal, it has failed to change chlorophyll concentrations in Lake Mead. The proposal now under consideration also appears to be headed for failure.

DEP also expects to impose restrictions on municipal discharges of ammonia. These phosphorus and ammonia restrictions are estimated to cost the taxpayers of Southern Nevada $110 million (including construction costs plus the present value of operation and maintenance over the next 20 years) .

The failure of municipal phosphorus removal may be compared to a field of grass. The height of the grass depends not only on the amount of fertilizer applied to the field, but also on the number of cows eating the grass. In the same way, the amount of chlorophyll in Lake Mead depends not only on the amount of phosphorus fertilizer added to the lake, but on grazing and other ecological processes. DEP has ignored grazing and other ecological processes. It is an oversimplification to suggest, as DEP does, that phosphorus from wastewater discharges controls the amount of chlorophyll in the lake. The data show that there is no relationship between the two.

Moving the point at which Las Vegas Wash enters Lake Mead might be more effective than investing in wastewater- treatment facilities. DEP and the U.S. Environmental Protection Agency (EPA), among others, have endorsed the concept. Advocates say that moving the discharge will spread the inflowing wash water over a much greater area, thereby eliminating the peak concentrations found in the inner bay. However, not enough is known about mixing and ecology in the bay to determine where to move the discharge, or to be certain that it will succeed. A study is needed.

If the proposed standards are adopted now, the local governments and their consulting engineers may soon have to decide whether to add wastewater-treatment facilities or to move the discharge. Under these circumstances, they are likely to opt for more treatment facilities—there is simply not enough known about moving the discharge to make the commitment now.

We propose a Coordinated Lake Mead Study (CLAMS), financed by the local governments, to investigate moving the discharge and to determine whether there is any problem caused by un-ionized ammonia. CLAMS is expected to last three years/ of which two years will be spent collecting data and the third year analyzing and interpreting them. It is expected to cost several hundred thousand dollars per year.

We request that any decision on the proposed standards be deferred until the next triennial review, so that CLAMS can be completed before standards are established. Nothing in law or science requires the Commission to set standards now. EPA staff has suggested that once the proposed standards are established, they cannot be relaxed, even if CLAMS should prove that they are wasteful and unnecessary.


Aquatic pollution; Ammonia; Chlorophyll; Environmental monitoring; Environmental protection; pH; Phosphorus removal; Water quality


Aquaculture and Fisheries | Environmental Health and Protection | Environmental Indicators and Impact Assessment | Environmental Monitoring | Natural Resource Economics | Natural Resources and Conservation | Natural Resources Management and Policy | Water Resource Management




The appendices to this report are published separately as Appendices to Analysis of the water-quality standards proposed by the Nevada Division of Environmental Protection, August, 1987.