Anoka and Rum River watershed officials plan to seek about $4.2 million in state bonds to upgrade the Rum River Dam to serve as a backup barrier to Asian carp.

They say the work is needed in case the voracious invasive species gets past the Coon Rapids Regional Park Dam, downstream on the Mississippi River.

The 10-foot-high Rum River Dam is the last major obstacle that could keep the fish out of the Rum, which originates 152 miles northwest at Lake Mille Lacs, a major state fishery, noted Anoka City Manager Tim Cruikshank. He said carp could swim through the 20-foot-wide sluice gate that is opened several times a year.

Work began this spring on a state-funded upgrade of the Coon Rapids Dam, which stands about six miles below the Rum-Mississippi confluence. This $16 million project also is aimed at stopping the Asian carp, which has been caught on the Mississippi as far north as Hastings.

The invader includes the Silver carp species, which can leap 10 feet out of the water and has whacked boaters in Southern states. Asian carp compete with native fish for microscopic food, such as algae.

Cruikshank recently discussed the backup barrier, which his City Council supports, at a meeting of the four member cities of the Lower Rum River Water Management Organization: Anoka, Andover, Ramsey and Coon Rapids.

The Rum River Dam in Anoka has a sluice gate that, when opened, could let fish pass through. The fear is that Asian carp could do so and head north to Lake Mille Lacs.

"We will seek legislative bonds" for an estimated $4.2 million dam upgrade, he told the watershed group at the Green Haven Golf Course clubhouse in Anoka.

"Once the [invasive] species gets up the river, the horse is out of the barn," Andover City Council Member Mike Knight said at the meeting. "You will never get him back."

Anoka's next step will be to apply for a $250,000 grant from State Lottery proceeds to study how to modify the dam to be an effective carp barrier, Cruik­shank said. Forty percent of lottery proceeds are designated for projects that preserve and improve Minnesota's environment and natural resources.

The study would provide engineering details and a firm cost for the upgrade. Cruikshank said later that the study would support the city's request for state bonding in the 2015 legislative session.

He asked the other watershed cities to support Anoka's grant request. He said watershed officials also will seek support from the 10 counties along the Rum. So far, the boards of the Lower Rum River and the Anoka Conservation District have approved a letter supporting the grant application. The Lower Rum board will consider paying up to $10,000 to hire Stanley Consultants of St. Louis Park to prepare the application, said board Chairman Todd Haas.

Good shape, but no carp barrier

Cruikshank noted that the existing 235-foot dam is in good shape and is expected to last about 30 years.

But it's not much of a carp barrier.

Fish can pass through when its underwater sluice gate is opened to allow maintenance or other work, three or four times a year, said city engineering technician Russ Zastrow.

In the spring, the gate is opened to lower the water level above the dam, so that workers can install a three-foot-high board wall that backs up the river to create a pool extending 13 miles upstream. The gate also is opened in the fall when the boards are removed.

The pool provides improved boating for fisherman and more than 175 upstream homeowners, 96 living in Anoka. Ramsey has 72 homeowners on the Rum, and Andover, eight. The pool is popular for pontoons and smallmouth bass fishing.

The dam loses effectiveness during very high spring-runoff flows, Cruickshank noted in his presentation. High flows reduce the drop between pools above and below the dam, making it easier for fish to jump over the structure.

Anoka bought the dam in 1935 from the Pillsbury Milling Co. The city maintained and repaired the wooden structure until 1969, when it spent $650,000 to build a concrete dam.

Cruikshank asked upstream cities to consider sharing $18,000 in annual dam maintenance costs by paying an amount based on what share of watershed land they cover. Ramsey occupies nearly half of that land, followed by Andover (27 percent) and Anoka (22 percent). Coon Rapids, which has a 2 percent share, is considering transferring that land to the Coon Creek Watershed, into which most of Coon Rapids drains.

"I am open to the idea of looking at how the dam is maintained," said Ramsey Mayor Sarah Strommen. "They threw one option up there. I'd prefer to back up and talk about if it makes sense to cost share and, if so, what are options."

Strommen said the carp barrier proposal is also worth exploring: "Certainly, we want to protect the Rum and Mille Lacs watershed from aquatic invasive species."

Jim Adams • 612-673-7658