Aquatic Nuisance Species

The Plants

By Lynn Schlueter, aquatic nuisance species coordinator, Devils Lake

Aquatic nuisance species threaten our fishing, boating, swimming, and other water-based resources.  In those states where they have become established, ANS have had untold negative effects.  They are expensive to combat, and in most cases where they have become established, they are difficult to impossible to control or eradicate.

Just what are aquatic nuisance species?  To name a few examples they are the ubiquitous carp, which can out-compete more desirable fish such as walleye, zebra mussel which can plug municipal water intakes, and Eurasian water-milfoil which can choke a lake, making it impossible to boat or swim. 

To prevent introduction of ANS into our waters, outdoor recreationists should learn to identify these species and pay heed to the equipment cleaning and bait guidelines at the end of this document.

• Eurasian Water-Milfoil
• Curly-Leaf Pondweed

Eurasian Water-Milfoil

• Eurasian milfoil infestations (39Kb GIF) or
• Eurasian milfoil infestations (576Kb PDF)

Grows in thick mats that shade out native plants.
- Produces a monoculture unfavorable to production of sportfish.
- Stunted fish can occur as a result of the heavy cover from predators.
- Late summer die-offs cause alga blooms, reducing dissolved oxygen needed by fish.

Native of Europe.
- Brought to northeastern US in 1880's.  Found in 33 states by 1985.
- Common in Minnesota and Wisconsin waters.
- One plant was found in N. Dak's. Sheyenne River in the 1990's, but none since.

Eurasian water-milfoil is a rooted, submerged plant seen in shallow waters.
- Stems reddish-brown to whitish-pink
  - One-eighth to one-quarter inch diameter
  - Up to five feet in length.
- Leaves deeply divided, soft, and feather like.
  - About two inches long.
  - Arranged in whorls of 3-6 leaves about the stem.
  - Leaves are limp when out of the water.
- Flowers reddish and very small.
  - Held several inches above the water when the plant is blooming.
  - After pollination, flower spikes sink under water.

Most infestations started by plant fragments growing into new plants or by root runners.
- Grows best on soft mud bottoms in waters with moderate nutrient levels.
- Survives for months under the ice.

Chemical or mechanical control is expensive and often unsuccessful.
- Native and desirable plants are also killed.
- Opens the area to recolonization by water-milfoil.

Eurasian water-milfoil would flourish in many North Dakota waters.

Sheyenne River boaters should watch for this plant and clean their equipment thoroughly.

Curly-Leaf Pondweed

• Curly-leaf pondweed infestations (75Kb GIF) or
• Curly-leaf pondweed infestations (577Kb PDF)

Grows soon after ice out and deprives later-growing plants of nutrients.
- Quickly establishes a monoculture unfavorable for fish and wildlife.
- Forms thick surface mats that inhibit boating, swimming, and wading.
- Fishing declines when mats cover much of the lake's surface.
- Mats increase escape cover for small fish in shallow waters.
  - As a result small fish are not cropped by predators in summer.
  - As late summer plant die-offs occur, small fish lose their protection.
    - Predators begin actively feeding on them in shallow waters.
    - Large gamefish become vulnerable to overharvest by anglers.   

Native to Eurasia and Africa.
- Imported into the United States as an aquarium plant in the early 1800's.
- By mid-1880's was established in many eastern states and had spread westward.
- Would do well in most North Dakota waters that are not extremely salty.
  - Common in Lake Audubon, Lake Sakakawea, and Missouri River.
  - Isolated populations are also found in a few small lakes.

Plant stems are typically 1-3 feet in length.
- Fall/Winter: grows with smooth leaves and can over-winter as an upright plant.
- Spring/Summer: leaves oblong, reddish-green, fine-toothed edges, three inches long.

Chemical control is expensive with no assurance of effectiveness and mechanical control causes seed pods to dislodge and float to new areas. 

Preventing the spread of ANS - Equipment cleaning guidelines:

Go here to find out about aquatic nuisance animal species.

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