Aquatic plants are not all bad

August 8, 2003

Invasive plants, milfoil and hydrilla… recent topics in the news more often than all the other lake-oriented issues put together. These headlines are great for building awareness of the alien threat to our lakes, ponds, rivers and streams. At the same time, however, they have led some people to believe all lake plants are bad. In extreme cases, folks have overreacted and taken very harmful actions - using illegal aquatic pesticides to kill valuable lake plants.

Because aquatic pesticides can be easily purchased through mail order catalogs and the Internet, there exists a perception that these chemicals are safe. Indeed, they are not! Pesticides can be hazardous to the environment as well as the applicator.

Herbicides (pesticides aimed at plants) may kill aquatic plants only for a season or portion of a season. And they are not necessarily effective against all plants. That means a pesky plant could survive a given herbicide application while beneficial native plants succumb to the treatment. This invites an even worse weed problem soon after treatment because the undesirable plant has an opportunity to spread to areas previously occupied by desirable plants!

Herbicides also pose risks to humans, especially when misused. Applying an herbicide in lakes or ponds calls for many responsibilities: determining whether waters are used for drinking or irrigation, notifying shoreland residents and choosing the right herbicide and applying it precisely at the correct dosage.

That's why applying these chemicals without proper permission is a serious legal offense. Most catalogs and other product information do not mention that Maine requires a permit to use them. Anyone wishing to apply pesticides to almost any lake or pond must get a permit from the Dept. of Environmental Protection (DEP) and an applicator's license from the Maine Board of Pesticides Control. However because of the risks, applications for aquatic pesticide permits are generally not approved for individuals; the only ones approved so far have been from state agencies because they have considered the larger lake management questions and have the needed resources for application and monitoring. Such was the case when the Maine DEP recently applied herbicides to Pickerel Pond in Limerick to treat an infestation of hydrilla.

The DEP and the Board of Pesticides Control have jointly investigated several incidents on various lakes where aquatic pesticides were illegally used. Camp owners paid fines for their actions.

Remember, most aquatic plants are beneficial to lakes. They are habitat for many creatures, nurseries for young fish, and they stabilize bottom sediments. If aquatic plants are a problem for lake users, people are allowed to hand-remove a swath of vegetation 10 feet wide out into the lake. This will allow a place to swim and a passage for boats. To do this, an owner needs to get a Permit by Rule from the DEP. Although a quick and simple process, the permit carries clear standards which must be met. For information about Permit by Rule or if you have questions, contact your nearest regional DEP office or check our web page at http://www.maine.gov/dep/blwq/stand.htm

To prevent the spread of invasive plants, rather than applying herbicides, remove all plants from your boat, motor, trailer, fishing gear, anchor, etc. before you float.

This column was submitted by Barbara Welch, Biologist and Outreach Coordinator with the Maine DEP's Bureau of Land and Water Quality. In Our Back Yard is a weekly column of the Maine Department of Environmental Protection. E-mail your environmental questions to infodep@maine.gov or send them to In Our Back Yard, Maine DEP, 17 State House Station, Augusta, ME 04333.