The War on Milfoil and How it Affects Fish

By now almost every boater, swimmer, water-skier, angler and just about anyone who uses New Hampshire water bodies knows what Milfoil is but just in case this is news to you I will try to explain what Milfoil is, how New Hampshire is trying to eradicate it and how it affects fish (and by extension, fishing).

What is Milfoil?

Milfoil, aka Eurasian Watermilfoil was first introduced to the eastern USA in the 1940’s as a plant to be used in home aquariums. It is a beautiful plant with feather-like leaves encircling a vine. When there is current, the feathers gently ebb and flow. Think about how beautiful the colorful fall leaves of a tree look when a subtle breeze is blowing them. Poems have been written about such beauty.

How does Milfoil affect water?

milfoil-3Once Milfoil found its way into native waters  it became an invasive species of plant that can radically change the ecology of the lake or pond in which it is found. It can grow at an inch a day if conditions are ripe, it forms very dense mats of vegetation on the surface of the water and it spreads so fast that a small body of water can be choked with it in a single season or two. The thick Milfoil mats interfere with most recreational activities including boating, swimming, water skiing and fishing. The sheer number of plants can cause currents to slow or even allow the water to become stagnant which in turn can create very good habitats for mosquitoes and with the world now aware of the ZIKA virus, this is not good for New Hampshire.

milfoil-4Besides giving mosquitoes a home, Milfoil mats are so substantial that they can prevent the oxygenation of the water by preventing of the wind from mixing the oxygenated surface waters to deeper water. Because Milfoil starts growing earlier in the spring it is a detriment to the native species of beneficial aquatic plants. The Milfoil will shade out the native plants making it harder for native plants to find conditions conducive to growing.

How does Milfoil spread?

milfoil-on-motorWhen boaters, skiers or other disturbances break the Milfoil, the fragments created will allow new plants to grow. In late summer and on towards the fall, Milfoil will become weak and naturally break apart. The fragments created naturally or by disturbances will float to other areas of the pond or lake where they will sink and start new plants. New plants can start from even a small fragment of the broken plant. This is why it is so important to check your boats and trailers for any evidence of the plant before launching into a body of water and after coming ashore from the body of water. Milfoil is easily transported from lake to pond to pond to lake on boat trailers and/or on fishing gear and once delivered to its new home, natural water currents will carry the fragments and the Milfoil will start new colonies. This is how Milfoil is able to reproduce and how it is able to travel from one body of water to another.

What is New Hampshire doing about Milfoil?

It is difficult if not impossible to remove Milfoil once it becomes established in a water body, so what is New Hampshire doing to combat this invasive plant? New Hampshire has instituted a program known as Weed Watchers. Weed Watchers are volunteers that have been trained to identify Milfoil and to report it to the proper officials. These are people who, when out on New Hampshire water bodies can spot and record outbreaks of Millfoil but cannot try to hand harvest the Milfoil themselves.  The Weed Watcher program has helped in keeping the problem of Milfoil in check.

weed-watcherNew Hampshire has also developed the “Lake Host Program” to combat Milfoil. Boat launches are monitored by Lake Associations, concerned property owners and others to try and prevent Milfoil from traveling. The common method of transportation for Milfoil is by boats brought from one body of water to another. I myself have come in contact with one of the hosts when my brother and I were fishing at Pawtuckaway Lake earlier this year. The host was quite congenial and openly asked every boater if they minded if he looked over their boat and trailer to make sure that there was no Milfoil openly visible on the vehicles. milfoil-signEven the slightest piece of Milfoil entangled in a boat propeller is enough to create a new infestation.

New Hampshire urges boat owners to inspect their equipment before placing it in a body of water. Signs at launches alert them of their responsibilities in keeping the lakes clean and Milfoil-free.


New Hampshire also treats certain water bodies with a chemical herbicide known as 2-4d, a chemical component known to not just defoliate but spread to the roots of the plant.  This chemical (2-4 d) is taken up through the root system of the plant very quickly and kills it, especially the crowns. You yourself may have been on a body of water where there seemed to be no vegetation. In these instances you can look down into the water and if it is clear you may even see dead plants on the bottom. Dead plants are a sure sign that the state may have chemically treated the body of water.

How does Milfoil and the spraying of herbicides affect fishing?

bass-milfoilAnglers and Bass both seem to love the advantages that Milfoil offers. It gives Bass a place to hide, giving them a sense of security from predators and it later provides shelter to the Bass Frye. Though fishing in Milfoil can be a challenge, it does allow anglers the ability to find and catch larger fish. It can be quite frustrating for anyone using a motor to navigate, but anglers using smaller boats and manual power have a much easier time getting into the thick of it.

Now when the State sprays to get rid of the Milfoil, the Bass can sense the changes created by the chemical. The bite will be off as Bass will begin searching for alternative living spaces. While you will still be able to catch some fish, the larger fish will usually be that much harder to locate and catch. After all, if someone was taking your home away from you, wouldn’t you be worried about finding a new home? I have fished a few bodies of water where the state had recently sprayed and though I caught a few fish, there was a noticeable decrease in the action.

If you can add any information, update or even disagree with anything I have said here, please leave a comment. By sharing information we can all become better anglers.

Tight lines, the Amateur Angler

Click on the flyer below to see the NH DES fact sheet regarding herbicide and Milfoil.


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