Hungry carp, spreading pondweed, multiplying mussels

Dan Bever, who has lived on Big Marine Lake since 1959, asked Doug Thomas and Jim Shaver about netting carp.
Dan Bever, who lives on Big Marine Lake, asked Doug Thomas and Jim Shaver about netting carp.

Watershed districts, county join forces to fight invaders

To keep lake and river lovers up to date on invasive species, speakers from Blue Water Science, the National Park Service, two local watershed districts and Chisago County teamed up to host a free workshop at the Scandia Community Center on Saturday, March 9.

Blue Water Science owner Steve McComas, author of “The Lake and Pond Management Guidebook” and of the Lake Detective newspaper column, was unable to attend.

Connor McComas
Connor McComas

Instead, his son Connor McComas filled in. Connor McComas has a degree in environmental science from Iowa State University and has worked with his father for 10 years.

He spoke about management options for curly leaf pondweed, Eurasian milfoil and common carp.

Byron Karns of the National Park Service talked about zebra mussels and other species.

The session was hosted by the Comfort Lake/Forest Lake Watershed District, Carnelian/Marine/St. Croix Watershed District and Chisago County.

A watershed district is a local unit of government authorized under Minnesota statute to conserve natural resources through land use planning, flood control, and other conservation projects. The political boundary of each watershed district follows the natural watershed and therefore may include parts of several cities.

The Comfort Lake/Forest Lake Watershed District covers 47 square miles in northern Washington County and southern Chisago County, the area that drains to the St. Croix River by way of the Sunrise River.

The Carnelian/Marine/St. Croix Watershed District covers 81 square miles in northeast Washington County: Marine on St. Croix, May Township and parts of Scandia and Stillwater Township. It includes 31 lakes and 17 miles of St. Croix River shoreline.

Doug Thomas of the Comfort Lake/Forest Lake Watershed District, Jim Shaver of the Carnelian/Marine/St. Croix Watershed District, and Jerry Spetzman, water resources manager for Chisago County, were on hand to answer questions.

More than 100 people turned up to see this collaborative presentation.

Common Carp

Native to Asia, carp are found throughout the lower 48 states.

Carp churn up muck at the bottom of a shallow lake, uprooting plants that other fish and waterfowl depend on for food.

Schools of carp make the water murky and release phosphorus that feeds algal blooms.

A hundred pounds of carp per acre of water dramatically decreases lake quality, according to Doug Thomas of the Comfort Lake/Forest Lake Watershed District.

So with carp, the goal is to get the number down and keep it down.

Two fish barriers were installed on Bone Lake in Scandia with that goal in mind.

Sunfish eat carp eggs. But recent studies have shown that carp can avoid sunfish by spawning in nearby wetlands, and the young  find their way back to the lake.

So another technique is to make sure they’re not spawning or overwintering in sanctuaries. “Carp is a very smart, long-lived fish,” Connor McComas of Blue Water Science said.

Commercial carp harvesters use nets to remove carp. There is a market for carp protein, but to make sure their costs are covered, a lake association may subsidize the operation.

Radio tagging was done on Clear Lake in Forest Lake. Driving a four-wheeler on the ice to pinpoint a few carp locates the school.

With prizes of $15,000 in cash and boats, fishing contests can be totally self-supporting, said Jerry Spetzman, Chisago County water resources manager.

People will come from all over the U.S. for these events, he said.

During the Chisago Lakes Lions Club carp tournament two years ago, competitors caught 1.5 tons of carp in North and South Center Lakes.

Now an annual event, this year’s tournament will be May 17 and 18 and will include Comfort Lake, Big and Little Green Lakes, North and South Lindstrom Lakes, Chisago Lake, Sunrise Lake, and North and South Center Lakes.

A drawing will be used to assign bow fishers to lakes,  said Steve Levey, the Lions Club member who started the tournament. Visit for the entry form and rules.

Curly Leaf Pondweed

In Minnesota for more than 100 years, curly leaf pondweed thrives in lakes with abundant nutrients.

Two lake qualities that lead to strong growth are high pH and organic matter over 20 percent, Blue Water Science’s Connor McComas said.

Curly leaf pondweed (photo from
Curly leaf pondweed (

Native to Europe and Asia, curly leaf pondweed has narrow leaves with ruffled edges.

Like native pondweeds, it grows submersed, generally in water that is less than 15 feet deep.

But unlike the natives, it has an extraordinary ability to propagate itself.

Curly leaf pondweed “comes in hard,” McComas said, and very quickly forms dense mats.

With superior overwintering strategies, it can out-compete native vegetation. “It gets a jumpstart in the spring,” he said.

In the fall, the plant forms buds called turions at the stem tips. Each turion can detach from the parent plant and remain dormant until spring.

Turions begin to grow as soon as light reaches the lake bottom—long before native plants.

That is why curly leaf pondweed growth in Forest Lake was so strong in the spring of 2012, according to Steve Schmaltz, president of the Forest Lake Lake Association: the meager snow cover that winter let in lots of light.

Turions can also grow after being carried to another body of water, which is one reason it is so important to clear all vegetation from boats.

In addition to being the first to grow in the spring, curly leaf pondweed also produces runners in April and May. McComas showed a picture of a small, single-stemmed plant, and one of a large, ugly mass of runners—two stages in the life of curly leaf pondweed.

The mat-like structure near the surface displaces native plants and interferes with boating, water skiing and swimming.

Then, just before the 4th of July, it dies and piles up on shorelines.

The dead plant releases phosphorus that feeds summer algae blooms. One pound of phosphorus can lead to 500 pounds of algae, Schmaltz said.

Forest Lake  has 2,300 acres of water, with 1500 acres under 15 feet deep.

Last year the Forest Lake Lake Association hired a firm to chemically treat 155 acres on May 9. The map shows the treated areas.

Areas with heavy curly leaf pondweed growth were identified in a survey conducted in April by Steve McComas, who was hired by the Comfort Lake/Forest Lake Watershed District.

The herbicide used against curly leaf pondweed, Aquathol, is applied in early spring before native plants are growing.

This year the plan is to treat 170 acres of curly leaf pondweed. The $37,000 cost will be shared by the city ($25,000) and the lake association ($12,000).

In June, the watershed district will pay $3,000 for an aquatic plant survey, required every five years by the DNR for lakes using herbicide to control invasive weed species.

The lake association also uses a mechanical weed harvester to remove plants.

The weed harvester is owned by the city of Forest Lake, which pays for fuel, maintenance and insurance. City staff put the harvester in the lake, haul weeds to the compost site,  and take the harvester out at the end of the season.

The lake association runs the harvester with volunteer labor and donates $2,000 a year to help with maintenance costs.

Schmaltz said mechanical harvesting was used for curly leaf pondweed in the past, before herbicides were introduced. “With no herbicide, the plant dies in July. Then we used the harvester,” he said.

“If you can kill it before it grows in the spring,” he said, “then no harvesting is necessary.”

The lake association still does weed harvesting to control channels, bays and boat launches. A path is cut through all vegetation (not just pondweed) so boats can pass.

A survey conducted each April locates areas of heavy growth. The operator uses the GPS coordinates noted by the surveyor to treat these areas.

Two weeks after treatment, the lake is surveyed again in case some areas need additional treatment.

People have expressed concerns about herbicide use, Schmaltz said, but the DNR has studied it for years and there are no known problems. To use herbicide requires a DNR permit and following DNR protocols. “There are a lot of controls,” he said.

Zebra Mussels

Byron Karnes
Byron Karnes

Byron Carnes of the National Park Service is an expert on the zebra mussel.

Under 2 inches long, he said, this invader originated in the Caspian Sea. By 1830 it had moved across Europe, and then came in Atlantic Ocean transport ships to the eastern Great Lakes. Zebra mussels were discovered in Lake St. Clair near Detroit in 1988.

In the veliger (larval) stage they float like plankton, but as adults they settle. “In the lower St. Croix,” he said, “we think they are attracted to native mussel beds in the river.”

Zebra mussels reproduce when the water is 55 to 60 degrees, several times each season, into September and October.

Factors that inhibit their growth include pH, water temperature, salt and calcium.

Karnes said a few northern lakes are so poor in calcium that they can’t support zebra mussels, but here the conditions are very favorable for growth.

The zebra mussel uses protein strands to grasp onto things. No native freshwater mussel or clam in North American has this feature, Karnes said.

Zebra mussels have economic, recreational and  biological impacts. Live ones cover boat propellers, even crayfish. As they die, they wash up on shore.

Adult zebra mussels settle onto a hard surface. This can be other zebra mussels, making a mat so thick that the ones underneath suffocate.

He showed a photograph of a pipe so full of zebra mussels that water could not flow, and said there are reports of pipes six feet in diameter, completely clogged with zebra mussels.

They can also settle onto a barge, which makes an ideal surface: flat, slow-moving, dark, creviced. From Texas to Minneapolis, they make the journey on the backs of barges.

Karnes showed inland waterway system maps from 1988, 1992 and 2000 that trace the growth of zebra mussels across the Mississippi River basin. A current map showed them also in the western U.S.

Zebra mussels were found in the St. Croix River in 2000, he said, with larger numbers downstream. In 2007 and 2008, at St. Croix Bluff Park near Afton, they numbered 10,000 per square meter. But in the last three years, zebra mussel populations have declined.

Predation is one reason, as fish like drum, carp and bluegills eat them.

Some very odd water years, with high river water in the summer, may be floating the veligers to the Mississippi.

Native mussels have strategies to get their babies upstream, Karnes said, but not zebra mussels. “They’re really a critter of lakes, not rivers.”

To help prevent further spread of zebra mussels, Karnes said, a task force created in the 1990s put together the 1993-1994 action plan, the first of its kind to include prevention.

Information and education, inspections and access management, active and passive monitoring, and remediation were components of the plan.

They got the message to boat owners and set up wash stations. Check stations manned with law enforcement turned boats around if zebra mussels attached.

Dry dock boat inspection was added to check boats that had been pulled out for the winter.

The deaths of hundreds of loons at Sleeping Bear Dunes National Lakeshore in Michigan last fall may have been related to invasive mussels, Karnes said.

Other invaders

Eurasian water milfoil spreads from small fragments: a floating chunk can resprout in a new location.

It is not in Forest Lake as of 2012 and soil conditions there do not support long-term heavy growth.

Jim Shaver of the Carnelian/Marine/St. Croix watershed district said Big Marine Lake is treated for Eurasian milfoil.

It was discovered in the lake in 2004, and the lake association, supported financially by the watershed district, has been treating it since 2009.

A systemic herbicide, such as 2,4-D or Triclopyr (which includes 2,4-D), is used for milfoil.

In Chisago County, Jerry Spetzman said, milfoil is controlled in navigation channels.

Shaver said his watershed district has had success controlling purple loosestrife, another non-native plant, by raising a species of beetles and releasing them into wetlands.

Flowering rush is a slow-growing, slow-spreading plant that has appeared in Forest Lake. It can block out native sedges. A potent invader, flowering rush spreads by horizontal rhizomes. Herbicides can be used for control; it is important to remove the entire plant.

How to fight invaders?

A thorough boat cleaning includes examining the boat and equipment, removing all plants and animals, rinsing, and draining all live wells, bilges and bait buckets.

In the summer, it takes about five days for a boat to dry, but in the fall it may take two or three weeks.