watermilfoil: fact sheet
Eurasian watermilfoil (Myriophyllum spicatum) is an invasive,
submersed (underwater) aquatic plant accidentally introduced in
the 1940s to North America from Europe, where it is widespread.
It most likely reached eastern North America through the aquarium
trade, entering the waters when aquarium owners released the contents
of their aquariums into local lakes. Eurasian watermilfoil flourished
and began to spread westward by clinging to recreational boats.
People using Lake Minnetonka near Minneapolis, reported the first
Eurasian watermilfoil infestation in Minnesota in 1987. Eurasian
watermilfoil now occupies over 120 water bodies throughout the state.
WHY IS EURASIAN WATERMILFOIL A CONCERN?
Eurasian watermilfoil can form thick underwater stands of tangled
stems and vast mats of vegetation on the water's surface, especially
in shallow, nutrient-rich water. These mats can limit boating, swimming,
and fishing. Milfoil generally does not produce mats on the surface
in water more than 15 feet deep, and doesn't usually grow in water
more than 20 feet deep.
Eurasian watermilfoil can disrupt the ecology of a water body by
crowding out important native aquatic plants needed for a healthy
fishery. It can potentially reduce property values. Under severe
conditions, property owners and lake associations can expect increased
costs to keep boat channels open by mechanical harvesting and for
costs associated with disposal of rotting vegetation. However, it
does not cause problems in every body of water where it is established.
In lakes with low water clarity, milfoil does not produce mats in
water more than six feet deep, if at all. In parts of lakes where
bottom fertility is low, for example in sandy areas, the growth
of milfoil and aquatic plants tends to be low.
See FACTS below for more information.
HOW DOES EURASIAN WATERMILFOIL SPREAD?
Eurasian watermilfoil plants spread naturally through stem fragments
and underground runners. Accidental cutting of the plants can start
new plants when the fragments are transported by watercraft or on
waves and currents to new areas where they can root and grow.
Aquatic weeds (macrophytes) caught on a boat trailer at a Lake St.
Clair boat access. Ladd Johnson NOAA/Great Lakes Environmental Research
HOW CAN YOU HELP PREVENT THE SPREAD OF EURASIAN
Eurasian watermilfoil may become tangled in boat propellers, transducers,
trim tabs, bow lines, fishing nets, and on trailers. Actions you
take as a responsible boater are critical in preventing the spread
of Eurasian watermilfoil to other Minnesota waters.
Before leaving a lake or river:
- INSPECT and REMOVE all aquatic plants and animals
- DRAIN water from motors, live wells and bait containers
- DISPOSE of unwanted live bait on land
- RINSE your boat and equipment with hot (104°F) high pressure
tap water or
- DRY your boat and equipment for at least 5 days
Line drawing of boat from the Minnesota DNR
WHAT ARE THE REGULATIONS ABOUT EURASIAN WATERMILFOIL
It is unlawful in Minnesota to:
For more information on Minnesota's prohibited species, look for the
the Waterfront: The Exotic Species Update" publication on the
Minnesota Department of Natural Resource's Web site.
- Transport aquatic plants, including Eurasian watermilfoil or
other prohibited species on public roads.
- Place a boat or trailer with attached aquatic plants or prohibited
species into Minnesota waters.
- Transport water from infested waters.
IS EURASIAN WATERMILFOIL IN A LAKE OR RIVER NEAR YOU?
For Minnesota, download the Minnesota Department of Natural Resources'
BE ON THE LOOKOUT!
Detecting infestations early, when they may be kept at manageable
levels, is important. Know where infestations are and learn to recognize
Eurasian watermilfoil. Report suspected milfoil infestations in
Minnesota to the Minnesota Department of Natural Resources (see
contact information below).
WHAT DOES EURASIAN WATERMILFOIL USUALLY LOOK LIKE?
- Submersed, rooted aquatic plant in shallow waters (less than
30 feet deep)
- Long branching stems near the surface with soft, feathery leaves
- Leaves usually attached in whorls of four, but sometimes 3-5
- Each leaf has 10-21 pairs of leaflets
- Leaflets are usually closely-spaced
- Leaves are limp when out of water
- Top of plants often turn red
- Small reddish flowers in mid summer
- Plants can grow up to 15 feet long
Eurasian watermilfoil is only one of six aquatic plants in the watermilfoil
family found in Minnesota. It is most commonly mistaken for native
Northern watermilfoil which has these characteristics:
- Leaves attached to stem in groups of 4 (rarely 5)
- Each leaf has 5-9 pairs of leaflets
- Leaflets are widely-spaced
- Leaves are rigid when out of water
- Plant does not branch at surface
IF YOU THINK YOU HAVE FOUND A NEW INFESTATION OF EURASIAN WATERMILFOIL:
Contact the Minnesota Department of Natural Resources at 651.259.5100
or (888) 646-6367 or mail them a sample of a suspected milfoil plant
in a sealed plastic bag.
Mail samples to:
Eurasian Watermilfoil Program
Ecological Services Section, Box 25
500 Lafayette Rd.
St. Paul, MN 55155-4025
CAN EURASIAN WATERMILFOIL BE ERADICATED FROM A LAKE OR RIVER?
Once Eurasian watermilfoil is established in a lake, it is nearly
impossible to eradicate. It does not cause problems in every water
body, but for those that it does, three of the most common measures
for managing nuisance growth are listed below. Most often, state
and federal agencies use more than one of these treatment options
to control Eurasian watermilfoil. Increasing public awareness about
infestations can help prevent further spread by boaters and anglers
to nearby lakes.
CONTROL OF EURASIAN WATERMILFOIL
of MN Biological Control Research)
3. Chemical Treatment
Of Eurasian Watermilfoil In Lake Minnetonka
WHAT ARE THE COSTS OF EURASIAN WATERMILFOIL CONTROL?
The Minnesota Department of Natural Resources spent approximately
$120,000 for maintenance management of Eurasian watermilfoil in
Impacts of Eurasian watermilfoil based on research:
(Facts compiled and presented by Larry Space and Joanna Wright, "The
Impact on Small Lakes of Vermont by the Invasion of Eurasian Watermilfoil:
A Property Owner's Perspective.")
- Increased boat repair and maintenance costs (One boat owner
in Vermont spent $800 repairing his boat when the motor intake
became clogged with milfoil)
- Declined native plant diversity (Madsen, et, al. 1991; Trebitz
- Depressed real estate values (Bates et. al 1985)
- Inhibited water circulation (Smart and Doyle 1995)
- Reduced levels of dissolved oxygen, enables nutrients to accumulate
creating unfavorable conditions for macroinvertebrates and fish
(Lillie & Budd 1992)
- Reduced density of invertebrates (fish food) (Keast 1984)
- Three to four times fewer fish versus native plant beds (Keast
- Caused significant increases in permanent pool mosquitoes (Bates
et. al 1985)
NEED MORE INFORMATION?
Lake Minnetonka Conservation District 1999 Eurasian Watermilfoil
Final Harvesting Report
Minnesota Department of Natural Resources 1999 Annual Report of
Harmful Exotic Aquatic Plants and Wild Animals in Minnesota
Help Managing Eurasian Watermilfoil in Minnesota
Nonindigenous Aquatic Species (NAS) Information Resource for the
United States Geological Survey
Vermont Department of Environmental Conservation