If you haven't gotten there yet this spring, there's still time. But hurry.

We refer, of course, to the show put on every spring in Damariscotta Mills. That tiny village is the site of one of the most thrilling displays of natural selection you're ever likely to encounter.

There, the fresh waters of Damaris-cotta Lake tumble down to meet the brackish waters of the aptly named Great Salt Bay, which is actually a bulbous protrusion at the head of the tidal Damariscotta River. And navigating upstream to spawn, from the Gulf of Maine through the Damariscotta River, Great Salt Bay and into Dam-ariscotta Lake, are tens of thousands of alewives.

What's thrilling is that it's not that easy a transition. There's no expensive fish elevator for alewives to get upstream from the top of Great Salt Bay to the lake, as there are on other rivers for finicky shad. There's no technically complex fish passage designed by the Army Corps of Engineers to usher these fish into fresh water.

Instead, there's an almost 200-year-old stone fish ladder that works just fine, thank you, and puts a lot of latter-day, fancy-pants fish passages to shame. The great clouds of alewives literally smell their way to this ancestral spawning ground, find the stream outlet on the western side of Great Salt Bay, cram through the abutments of a railroad bridge and squeeze even further into the tiny entrance of the fish ladder. Then, it's just 42 vertical feet up, and they've made it into Damariscotta Lake, where they'll reproduce.

That is, if they've made it that far. The tough ones make it, the less tough ones end up a feast for the dozens of osprey, cormorants, bald eagles, herring gulls, raccoons and all manner of other predators that show up every spring just like the alewives.

So these small, coppery fish -- a member of the herring family -- fight their way upstream, nosing and thrashing up the fish ladder's runs and resting pools, always, always, in the company of thousands of their fellow alewives.

Children love them. Adults love them. There are people who make the pilgrimage every year to see the great migration. Like the fish, they start at the bottom of the ladder. But unlike the fish, they walk their way up to the top, where they witness how, one by one, the strong and tenacious fish will rest, then shoot through the slot and into the lake.

That is, if there's no loon or largemouth bass waiting for 'em. Darn! Such is life, such is the cycle of life, such is the thrill of watching one of the most fundamental dramas on earth, fish version. Get thee off to Damariscotta Mills soon; you don't want to miss it.