Severe drought arrives just as young alewives should be leaving the lakes

Severe drought now covers just under half of Kennebec County.¹ A week ago it covered under seven percent.¹ The U.S. Drought Monitor map for the week ending September 7 moved most of the county from moderate to severe drought in a single step, and the way it got there matters: the county was merely abnormally dry in mid-July, went to moderate drought across nearly all of its area by the first week of August, then sat at that level for three straight weeks before tipping over.¹ Moderate drought or worse now covers 98 percent of the county, every acre of it is at least abnormally dry, and none of it has reached extreme drought.¹ A jump like that is less a new weather event than a running deficit finally crossing a line; the dryness underneath it has been building since early August.¹

What gives it teeth here is the calendar. The Sebasticook River, which passes Burnham and Clinton on its way to the Kennebec at Winslow, carries the largest alewife run in the country, roughly a few million adults a year over the Benton Falls fish lift since the Fort Halifax dam came out in 2008, with a peak of 5.7 million in 2018.² Those adults spawned in Unity Pond and Sebasticook Lake in May and June and went back to sea. Their young have spent the summer in the lakes, growing from something that looks like a mosquito larva into a silver fish one to three inches long, feeding on zooplankton and, in the process, carrying phosphorus out of lakes that both already sit on the state's impaired-waters list.³

Late August through September is when the young fish leave, and they leave in pulses. The Maine Department of Marine Resources describes fall rainstorms as the trigger that sends them out of the lake outlets in dense schools toward Benton Falls and the sea.⁴ A dry September removes that cue. Maine fish-passage programs name drought as one of the main hazards for exactly this size class at exactly this season, because juveniles that never get the signal stay in warm, food-limited lake water longer, and juveniles that do move through low water bunch up at every constriction, where eels, herons, mink, otters and eagles already hunt them each fall.⁵

Whether this year's cohort is running on schedule is not something anyone has counted; the fish lift tallies adults in spring, not juveniles in fall. What can be said is that the county crossed into severe drought in the same week the young alewives would normally be starting to go.¹ Anyone who wants to see the run should watch the lake outlets and the tailrace at Burnham after the next real rain, and look for a moving raft of finger-length fish, not scattered individuals.

Sebasticook Regional Land Trust, which started as Friends of Unity Wetlands and later absorbed the Sebasticook River Watershed Association, runs paddles above the Burnham dam and bird walks at Unity Pond, and its Moulton's Mill Preserve in Unity sits on Twenty-five Mile Stream, one of the feeders of this system.