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Updated Apr 10, 2023

How to minimize the risk of pesticides entering waterwAYS

The photo shows irrigation water from a sloped lawn area flowing into the storm drain.

This situation poses risks to waterways.

  • If weed killer (herbicide) or insecticide was recently applied to the area, it could enter waterways.
  • Pesticides in waterways harm aquatic life such as frogs and invertebrates.
  • Fertilizer from lawns and landscapes can also harm waterways. Fertilizer in waterways causes algae blooms. When the algae dies, it leads to stagnant water (eutrophication).

What are pesticides?

Pesticides are products designed to kill rodents, weeds, mosses, insects, plant diseases, slugs, and snails. Household disinfectants such as bleach and ammonia are considered pesticides. Flea-killer products are too.

JUMP TO

  1. Understand How Pesticides Get into Waterways
  2. Pay Attention to Weather Conditions
  3. Read the Label & Follow the Instructions

FOR QUESTIONS ABOUT PESTICIDES

The National Pesticide Information Center (NPIC)  can answer questions about pest control chemicals.
 1-800-858-7378 or npic@ace.orst.edu  

Overview

  • Pesticides applied to landscapes can move to waterways.
  • These chemicals can mix with water from irrigation or rainfall. They can also move with the wind. Some can turn into a vapor on hot days.
  • Pesticides applied to land can leach through the soil into groundwater.
  • Pesticides may also flow into storm drains. Storm drains often connect to creeks, rivers, lakes, or the ocean.
  • Water in storm drains rarely gets treated. Even when the water goes to a treatment plant, most pesticides remain in it. Wastewater treatment plants aren’t designed to remove them.
  • Pesticides that run off from landscapes can have an impact on our drinking water, recreation areas, and aquatic life.

Keys for Success

  • Use information provided on pesticide labels to understand the risks of a product.
  • Look for information about hazards to waterways in the ENVIRONMENTAL HAZARDS section of the pesticide label.
  • Follow the instructions to minimize risks and maximize benefits.
  • Avoid quick release fertilizers; use slow release instead.
  • Don’t fertilize after May and if possible, wait until fall after Labor Day.
Salmon jumping in stream

Brandon (@greener_30) on Unsplash

Our Top Tip

Don’t dump pesticides or rinse water into storm drains. This is illegal. Poor handling and use of pesticides pollutes drinking and surface waters. Dumping pesticides into a drain is harmful to people and the environment.

UNDERSTAND HOW PESTICIDES GET INTO WATERWAYS

PESTICIDES MOVE WITH WATER & AIR

  • Pesticides applied to landscapes may travel into water via irrigation or rainfall. They can also leach into groundwater and flow into storm drains.
  • Pesticides that move into waterways may reach levels that can harm creatures living in the water.
  • Urban areas have hard surfaces that shed and transport water. These hard surfaces include pavement and roofs. Hard surfaces reduce the water’s ability to soak into the ground and increase runoff.
Landscape worker mixing pesticides in street gutter

Western IPM Center Water Quality Protection Project

Mix pesticides away from hard surfaces and storm drains. Never mix or apply pesticides in the gutter as shown in the photo. This can contaminate water and is illegal.

Irrigation water from lawn area moving into the gutter

Western IPM Center Water Quality Protection Project

Don’t let runoff from irrigation move off the landscape into waterways. The water can move pesticides applied to the landscape area.

Erosion of soil from irrigation problem

Weston Miller, Oregon State University

Pesticides attached to soil particles will travel with eroding soil. The amount and speed of water runoff determine how much erosion occurs.

Demonstration of blue-dyed liquid leaching down into soil

Kansas Geological Society

Pesticides can leach into the water table due to natural water movement from rain, snowmelt, or too much watering. The photo shows a simulation of liquid with blue dye leaching through the soil profile.

 

Paved surfaces and sidewalks can contribute to pesticide runoff

Western IPM Center Water Quality Protection Project

When pesticides get into water, hard surfaces enable the chemical to travel into storm drains and waterways. Concrete, decomposed granite, stone, and asphalt can carry chemicals some distance.

Managed lawn next to lake and trees

Western IPM Center Water Quality Protection Project

Pesticides applied next to a body of water can drift in air or flow with water into the surface water. The photo shows a lawn adjacent to a lake. Take steps to prevent pesticides from entering the waterway if you manage a similar site. See section 4.

Vapor in air

yudhistirama, iStock

If a pesticide is applied to soil or plants as a granular product or spray, it may turn to vapor. Then it may be carried off-site through the air and drop into nearby water.

PAY ATTENTION TO WEATHER CONDITIONS

Check the weather before making a pesticide application. Only apply pesticides when the weather conditions are favorable based on instructions on the product label.

Raindrops falling on flooded concrete and asphalt

Western IPM Center Water Quality Protection Project

Check to see if rain is in the forecast. Don’t apply pesticides when heavy rainfall is predicted in the next 48 hours. The water will wash the chemicals away and fail to control pests.

Low-lying layer of clouds indicates a temperature inversion

Western IPM Center Water Quality Protection Project

Never spray during an inversion. Don’t apply spray when you see clouds or smoke at a low ceiling. These are signs of a temperature inversion. An inversion occurs when cold air is near the ground with a layer of warm air above it. Spraying during an inversion increases your risk of exposure to chemicals. Watch the weather forecast for predictions of inversion. Avoid applying pesticides at those times.

Wind blowing across lake

Western IPM Center Water Quality Protection Project

Don’t spray on windy days. Wind can carry pesticide sprays into bodies of water. Herbicides carried by the wind may harm plants you did not intend to spray. Beware of random gusts that can cause drift. Never apply chemicals if the wind is blowing more than 10 miles per hour.

Photo of hot dry day in the high desert

Western IPM Center Water Quality Protection Project

Don’t apply pesticides in hot and dry weather. Time your pesticide applications to avoid hot and dry periods. High temperatures and low humidity increase vaporization (chemicals turn into gases). Some weed killers (herbicides) can turn into a vapor and damage nearby plants.

Some weed killer (herbicide) products become a vapor on hot days and can injure nearby plants. People have been sued for damaging farms, vineyards, and gardens. Ester forms of 2,4-D, triclopyr, and similar herbicides can vaporize on hot days. Check the label for temperature limits. Don’t spray when it’s hot, or when hot weather is expected within 1-2 days.
READ THE LABEL & FOLLOW THE INSTRUCTIONS.
  • The law requires you to read and follow pesticide directions.
  • To protect water quality, make sure you understand the environmental warnings.
  • Look for the ENVIRONMENTAL HAZARDS section on the product label. The section is often inside a booklet or pamphlet.
  • Look for the DIRECTIONS FOR USE section of the product label. Follow the instructions.
  • Calibrate your pesticide application equipment. Make sure you apply the right amount.
Gloved hands holding herbicide package to read label

Weston Miller, Oregon State University

Read the entire label front to back. Follow the instructions. Review the instructions even for brands you know. Only apply the product where the label says it can be applied. Keep all pesticides in their original container.

Gloved finger pointing to application rate table on pesticide label

Weston Miller, Oregon State University

Follow the product application timing and rate schedule stated on the label. It is illegal to use more pesticide than the amount stated on the label. It’s also illegal to apply pesticides more often than stated on the label. Over applying does not improve performance.

Learn How to Calibrate Your Sprayer

Calibrating a backpack sprayer enables you to apply the correct amount of a pesticide over an area.

See instructions on How to Calibrate a Backpack Sprayer  (Penn State University).

Content provided by Weston Miller and Kaci Buhl. Information sourced courtesy of Western IPM Center Water Quality Protection Project  

 Peer reviewed by OSU Department of Horticulture.

Photo of Weston Miller

Weston Miller

Project Founder and Content Writer

Weston Miller served as Community and Urban Horticulture faculty for Oregon State University Extension Service for Clackamas, Multnomah, and Washington Counties. Weston is an author for content for this website. He developed funding partnerships with Portland area agencies to initiate and build out the Solve Pest Problems website focused on this goals:

Photo of Kaci Buhl

Kaci Buhl

At the state level, I lead the Pesticide Safety Education Program (PSEP). The program hosts live recertification events around the state, serving over 1,000 licensed pesticide applicators each year. We also produce web-based training modules and license-preparation study manuals. Special training for unlicensed pesticide applicators is also available through a grant from the USDA Specialty Crop Block Grant Program. The PSEP at OSU works closely with the Oregon Department of Agriculture's Pesticides Division.

Pesticides and Water Quality References

Pesticide Environmental Stewardship  
eXtension

Safe and Effective Use in the Home Landscape  (UC ANR Publication 74126). Also available in Spanish as Pesticidas: Uso Seguro y Eficaz en el Hogar y en Jardines  

Also consult the UC IPM WaterTox  database, which provides information on the potential impacts of pesticides on water quality.