NOBLEBORO – Chuck Reinhardt stood in awe as he gazed down at the multitudes of silver-sided fish crowded into a waterway no more than 5 feet wide.

After three to four years at sea, thousands of alewives were following their instincts on a journey back to the freshwater where they were born.

The fish crammed themselves into a man-made brook on the final leg of their trip to Damariscotta Lake, reminding Reinhardt of a familiar scene before he moved to Maine.

“It looks like the Long Island Expressway,” he joked.

Each spring, tens of thousands of alewives pass through the historic Damariscotta Mills fishway, created in 1809 to allow the fish to bypass a series of waterfalls as they struggle upstream toward the lake, 54 feet above sea level.

The annual spectacle attracts hundreds of visitors.

It also attracts sea gulls and other birds in search of an easy meal. Ospreys hover overhead like helicopters before plunging down and grabbing fish with their talons, while hundreds of noisy gulls line the banks fighting over fish they’ve plucked from the water.

Cormorants, along with an occasional harbor seal, strike from below, causing the water to erupt in a frenzy of fleeing fish.

Alewives may be appetizing to birds, but they’re seldom found on Mainers’ dinner plates. Lobstermen use them as bait, forking over $60 for their four-bushel allotment, and the fish have been used in the past as fertilizer.

Still, a handful of people are known to eat smoked alewives, a bony fish with a sweet, white flesh.

All of the hoopla at Damariscotta Mills typically starts in May when the water hits 56 degrees, said Frank Waltz, who has worked the alewife run for 45 years.

Waltz, a familiar sight in his green waders and train engineer’s cap, manages the fishery along with Dale Wright for Nobleboro and Newcastle, the two towns bisected by the stream that runs between Damariscotta Lake and the ocean.

This year’s alewife run was delayed by a miserable stretch of cold, rainy weather. When the sun returned, it warmed the water and triggered a massive migration.

Shortly after sunrise on the last Sunday in May, Wright stood on the Mills Road Bridge smiling like a kid as swarms of fish passed underneath.

“They came in the night before last. This is like Christmas to me,” he beamed.