WORTHINGTON - Nearly half of the floating biohavens placed in Sunset Bay as a way to help improve water quality will need to be replanted thanks to the efforts of some pesky Canada geese.

Seven of the 15 islands have been picked clean by the geese, leading some to complain to the Okabena-Ocheda Watershed District about their appearance. Last week, watershed board members directed their administrator, Dan Livdahl, to order new plants to install on the floating biohavens.

The watershed district began experimenting with the biohavens in 2013, when 10 of them were placed on the E.O. Olson stormwater pond on the Minnesota West Community and Technical College campus. Two years later, the first of 15 biohavens were planted and anchored into Sunset Bay.

Livdahl said the islands in the stormwater pond look considerably better, as they haven’t been bothered as much by the geese. One biohaven there did get beached this spring after it broke free from its anchors and the water receded. It will need to be returned to the water and anchored once again.

As for the biohavens in Sunset Bay, fencing was installed on each of the islands before they were anchored in the water. But, over time, the wire mesh failed to keep the geese from climbing onto the islands to reach the lush green plants they held.

Livdahl removed fencing from several of the islands in Sunset Bay in June 2018, as they were no longer effective and looked “really ugly.”

“Unless you can keep fence on them and the geese off, they’ll pick everything clean,” Livdahl said.  “The ones that got picked clean never got re-established.”

Just this week, Livdahl said he watched a pair of geese lounging around on one of the floating islands and eating all of the new vegetation that had greened up.

Livdahl hopes to get new plants ordered and planted on the floating biohavens in early June. However, there are some challenges to doing so.

With increased rains and runoff from nearby lands, the water depth in the bay is at least 5 feet under some of the islands. Add in the muck at the bottom of the bay, and someone standing in one spot for too long could sink in a couple of feet. With no boat landing into Sunset Bay, walking in with waders or using a canoe are about the only options, and neither one is great.

“You can’t really work on an island where they’re floating,” Livdahl said. “Once they’re anchored, you have to pull them to shore, work on them and pull them back out again.”

That will have to be done for each of the seven islands, requiring considerable manpower. Livdahl will be in need of some volunteers to help once the plants arrive.

Each floating biohaven holds approximately 100 plants, and the plan is to replant them with varieties shown to have grown well on them in the past. These include sedges, reeds and prairie grasses.

Because the roots of the plants grow through the biohaven and into the water, they are locked in solid ice for the winter. That has impacted survivability - particularly of the prairie flowers, which didn’t survive their first winter.

“We’ve had the best luck with swamp milkweed,” Livdahl added. “If we’re looking for vegetation to survive long-term, we’re looking at sedges, reeds and prairie grasses that can survive tough conditions - wet conditions.”

Each spring, Livdahl said the islands look terrible until new plant growth begins. Since he doesn’t plant early season grasses on them, it takes a while.

In addition to doing the replantings and installing fencing, Livdahl said the rocks initially placed on the islands to weigh them down so plant roots could reach the water will also be removed. Over time, the islands have sunk lower in the water.

The biohavens were purchased and installed in Sunset Bay and the E.O. Olson stormwater pond in hopes of filtering out some of the phosphorus before it reaches Lake Okabena.

The local lake is on the state’s impaired waters list due to high levels of phosphorus.

“The Minnesota Pollution Control Agency came up with their Total Maximum Daily Load study, which said we needed to remove about 4,300 pounds of phosphorus annually from the lake if we’re going to get the lake off the imparied waters list,” Livdahl said. “Each of those islands, if everything is going well, could remove about a half pound of phosphorus per year. You would need 8,000 islands to bring the lake off the impaired waters list.”

Once phosphorus is in the water, it’s very difficult and very expensive to remove, he said, which is why the watershed district is taking a multi-pronged approach to reduce phosphorus levels. In addition to the floating islands, the district created stormwater ponds upstream at the former Prairie View golf course, and their next project is to do removal of carp from the lake.

“We’ve been telling people there’s no one activity - not floating islands, not Prairie View, not stormwater pond - is going to remove phosphorus from the lake,” Livdahl said. “It’s going to be many small practices over time. We’re trying to undo lake degradation that has happened over a long period of time.”