CONCORD, N.H. — New Hampshire’s loon population is up slightly from about a year ago, but the aquatic bird known for its eerie call is still threatened in the state, particularly at Squam Lake, where just a single chick hatched this year, preliminary numbers show.

Squam is one of the state’s largest lakes and the site of its worst decline in the loon population, according to the Loon Preservation Committee. Loons have been on the decline there since 2005. Before then, about eight out of a dozen chicks that hatched would survive.

Committee executive director Harry Vogel said early numbers statewide total just under 300 pairs of loons, slightly higher than last year. The numbers are down, however, for pairs that are nesting and for chicks that have hatched and survived.

“The growth of our loon population now is proceeding, but it’s proceeding painfully slow,” he said.

North America is home to five species of loons. The common loon is the most widespread and well-known, and the only one that breeds as far south as New Hampshire, the committee says on its website.

At Squam Lake, numbers have reached a “new and very depressing low,” said Tiffany Grade, a committee biologist.

“We’ve never had it before in all of our 42 years of monitoring on Squam where only one chick has hatched on the entire lake,” she said.

Grade and other biologists point to a combination of factors that make Squam Lake different from others. Those factors include the use of lead fishing tackle that poisons the birds, increased boating and fishing, and turf wars among migrating loons. Research from the committee also shows elevated levels of chemicals found in loon eggs and in soil samples from lake tributaries.

Loons are at the top of the aquatic food chain.

“So we knew that everything that was affecting the loons affects everything else that lives in the lake,” she said.

An administrator with the state Department of Environmental Services agrees the chemical levels are connected to the water fowl’s health.

“Unfortunately, this is one of these cases in which there is a legacy of contamination that we as humans have left in our wake,” said Ted Diers, administrator for the department’s Watershed Management Bureau. “It’s not clear that there’s an action that can be taken directly in the watershed. What we do next is really going to come out of some conversations between the organizations and the agencies working around Squam Lake.”