Background

The Clean Water Act, enacted in 1972 and later modified in 1977, 1981, and 1987, established
water quality goals for the navigable (surface) waters of the United States. One of the
mechanisms for achieving the goals of the Clean Water Act is the National Pollutant Discharge
Elimination System of permits (NPDES), which is administered by the Environmental Protection
Agency (EPA). The EPA has delegated responsibility to administer the NPDES permit program
to the State of Washington on the basis of Chapter 90.48 RCW, which defines the Department
of Ecology’s (DOE) authority and obligations in administering the wastewater discharge permit
program.

Timeline of Washington State Irrigation Permits:

The first Washington State Department of Ecology Irrigation NPDES general permit (WAG-
991000) was issued in 2002 and renewed again in 2007. In 2010, a modified NPDES permit
was issued allowing for the addition of two endothall products, Cascade (dipotassium salt of
endothall) and Teton (mono (N, N-dimethyl alkylamine) salt of endothall. Cascade is a product
used exclusively to control vascular plants while Teton (in addition to controlling vascular plants)
can be an effective algaecide. Irrigation districts operated under the modified 2010 NPDES
permit through 2012, when it was again renewed for a five-year term. In 2017, the DOE placed
the 2012 permit under an administrative extension while Ecology worked to draft a new permit
and develop an Environmental Impact Statement. In October of 2023, DOE issued the current
Irrigation System Aquatic Weed Control (ISAWC) NPDES permit.

Importance of Plant and Algae Control:

Irrigation districts encounter many obstacles while delivering irrigation water to landowners. An
irrigation conveyance system is dynamic in nature and if unmanaged, aquatic vegetation can
proliferate throughout the entire system. Constant changes require vigilance amongst staff while
carrying out water management strategies. Submerged vegetation limits carrying capacity,
reducing the amount of water available to deliver for agricultural production. Capacity issues
result in higher water levels which jeopardize the structural integrity of canals. These conditions
not only cause operational difficulties, but they also create safety hazards, placing people and
property in danger.

Treatment Plans and Strategies

Acquired knowledge through years of experience assisted the District in developing and
administering an Integrated Vegetative Management Plan. Using this plan, staff implement
specific water management strategies to best utilize all tools available to ensure delivery of
irrigation water to landowners while maintaining the structural integrity of district facilities. This
program includes mechanical, biological, and chemical means to control undesired vegetation
within our facilities. Since 1992, in an effort to provide an environmentally friendly method to
control vegetation, the East district has deployed triploid (sterile) grass carp in favorable areas.
The District operates the grass carp program under a Washington State Fish and Wildlife fish
stocking permit. With an aim at increased water conservation, the district also pipes conveyance
facilities. This has the additional benefit of removing the habitat conducive for nuisance plants
and algae to survive.


Authorization to Use Pesticides.

The District operates under a Washington State Department of Ecology Irrigation System
Aquatic Weed Control NPDES permit. Every five years this permit goes through a renewal
process where it is modified using the latest scientific data to protect sensitive species of plants
and animals. Under this permit, the District is authorized to use permitted pesticides to control
aquatic weeds and algae in irrigation systems that flow to surface water of the State of
Washington. The District must follow stringent NPDES discharge criteria and comply with Fish
and Wildlife timing windows for sensitive species.