A small park in Minnetonka has become a major battleground over Minnesota's new state bee.

Lone Lake Park has become a haven for the rare bumblebee on the brink of extinction, and the city's plan to build a mountain bike trail there is meeting fierce opposition. State courts have already ruled against a group of Minnetonka homeowners and park users who fought the new bike trail and demanded the city first conduct an environmental assessment.

Now, with construction on the trail set to start Sept. 1, a national environmental group has entered the fray.

The Center for Biological Diversity on Wednesday announced its intent to sue the city of Minnetonka in federal court for failing to protect the rusty patched bumblebee and violating the Endangered Species Act. The group estimates the 4.7-mile bike trail at the park will take out about 6 acres of critical habitat for the fuzzy striped insect, a docile bee whose numbers have plunged.

"Every single remaining population of Minnesota's state bee is absolutely critical for its survival," said Collette Adkins, a Minnesota-based senior attorney for the Center for Biological Diversity. "We're hoping to convince the city to do the right thing."

The two parties have set up a meeting for later this week, Adkins said.

A rusty patched bumblebee on Joe Pye weed.

The notice of intent is a step required by the Endangered Species Act. According to the notice, the city must develop a habitat conservation plan and apply for an "incidental take permit" from the U.S. Fish and Wildlife Service within 60 days.

The city declined a request for an interview. In a statement, it said it is still studying whether the permit is required, and is developing a mitigation plan to address potential impacts of the bike trail on the bee habitat.

"The city hired Barr Engineering to prepare a biological assessment of the area and the University of Minnesota is conducting a bee survey," the statement said. "The city also continues to consult closely in this effort with the U.S. Fish and Wildlife Service, the federal agency that oversees implementation of Endangered Species Act requirements."

Once that work is done, the city will decide whether federal law requires the permit and habitat conservation plan, it said.

Adkins said her group is not trying to stop the mountain bike trail. Instead, it wants the city to develop a plan to mitigate impacts on the bees. For example, the city could create additional habitat, such as converting areas with mowed grass to patches of wildflowers that provide the nectar the bees need. Joe Pye weed, Culver's root, bee balm and goldenrod are some favorites.

The timing of the project is also critical, she said. Construction shouldn't disturb flowers from March to October, she said, when the bees are most active and feeding. During winter, when the bees move underground, there shouldn't be digging in deeper areas of the forest.

The 146-acre park has woodlands, wetlands and prairie, as well as walking and biking trails and sports facilities including pickleball courts and a soccer field.

It's also designated a"high potential zone" for the rusty patched bumblebee, according to the Center for Biological Diversity. Research suggests the Lone Lake Park population represents 13% of the bee's total population in the state now, and 6% of the remaining population in North America.

The plump bee is identified by a rust-colored patch on its back. And while it doesn't make honey, it's an important plant pollinator. It's not clear exactly what's driving the bees' rapid die-off, but habitat loss, pesticides and disease, among other things, are considered factors.

The park is estimated to be home to the third largest known population of the bumblebees in the state, Adkins said.

The other two are Noerenberg Memorial Gardens in Orono, and the Minnesota Zoo.

The rusty patched bumblebee became the Minnesota state bee in 2019.