The population within the Belgrade Lakes watershed has declined over the last 10 years, one of several findings in a new report from Colby College on the 13 towns in the region.

With more than a third of the homes owned by seasonal residents, the trend is unlikely to reverse itself any time soon.

The population within the watershed declined by 553 people, or 5.3 percent, between 2000 and 2010. At the same time, the overall population in Maine rose by 4.2 percent.

The overall populations of Kennebec and Somerset counties also rose during the study period.

The reason is that the proportion of seasonal homes is growing, leaving fewer year-round residents in the region, according to the study’s lead author Michael Donihue, who is a professor of economics at Colby in Waterville.

“This would seem to confirm anecdotal reports that lakefront property is being purchased by people whose primary residents lies outside the Belgrade Lakes Watershed,” Donihue wrote in the study.

In the watershed, 34 percent of the total housing units are seasonal homes; the number is 16.4 percent in Maine, 21.4 percent in Somerset County, and 10.1 percent in Kennebec County.

The watershed comprises East Pond, Great Pond, Long Pond, McGrath Pond, Messalonskee Lake, North Pond and Salmon Lake.

The communities in it are: Augusta, Belgrade, Mercer, Manchester, Mount Vernon, New Sharon, Norridgewock, Oakland, Readfield, Rome, Sidney, Smithfield and Vienna.

Donihue said the report is part of a larger effort to assess the economic value of the lake system to the region.

The report includes a demographic profile that notes some other differences between those living in the watershed, and those in the surrounding areas.

The number of homes grew less quickly than surrounding communities, and the number of families showed a greater decline.

Those who live in the Belgrade Lakes region are likely to be better educated and better paid, than their counterparts in the state as a whole, and in Kennebec and Somerset counties.

About 28 percent of those 25 and older have a college degree, as opposed to 26 percent in the state as a whole, and less than 19 percent in Somerset County.

The median household income in the region is $52,699, 12 percent higher than the state average of $46,933. The number of households with incomes of more than $200,000 is 3.15 percent, higher than the state as a whole and more than double Somerset County, which is at 1.23 percent.

The 25-page-report is expected to help local and regional officials to understand the environment as it related to economic development throughout the region.

It was prepared by Donihue and students Nicholas Papanastassiou and Caitlin Vorlicek as part of Colby’s Belgrade Lakes Watershed Sustainability Project.