Everything's ready for migratory alewives to return to Rogers Lake in Old Lyme for the first time in several hundred years - the gleaming new concrete-and-steel fish ladder's open, the water's flowing through it and electronic fish counter is poised to start clicking away.

Now it's up to the fish to find their way there.

"I think it's just a matter of time," Steve Gephard, head of the Inland Fisheries Division of the state Department of Energy and Environmental Protection, said Thursday as he crouched next to the 20-foot ladder, beside the chamber housing the counter.

His confidence comes from watching the success of other fish ladders and dam removal projects across the state at restoring migratory fish runs. Typically, he said, it takes a few years after a ladder opens before alewife, blueback herring and shad start returning en masse. Those successes, along with the ecological importance of anadromous fish - those that divide their time between fresh and salt water environments - will be highlighted Saturday during World Fish Migration Day, a first-ever international event.

DEEP and The Nature Conservancy are sponsoring 16 events across Connecticut. Worldwide, 49 countries are hosting 257 events, including 66 in the United States, according to Pao Fernández Garrido, spokeswoman for the event and staff member at a Dutch water resources consulting firm, Wanningen Water Consult, that is one of the event's founding organizations.

The event has its origins in a Fish Migration Day first celebrated in the Netherlands in 2003, she said. This evolved into Living North Sea Fish Migration Day in 2011. Basically, said Sally Harold, director of river restoration and fish passage at the Nature Conservancy's Connecticut chapter, the purpose of the event is to build appreciation for what's been done to remove obstacles to migrating fish, and support for tackling the challenges that lie ahead.

"If we're going to succeed at getting more dams removed and more fish ladders built," she said, "we're going to have to have more people aware. We've had tremendous results. Every time we reopen a habitat, we see an increase in the runs."

Harold will be joining Gephard in a presentation Saturday morning about anadromous fish biology, dam removal and fish ladder projects at Lyme-Old Lyme High School.

After the program, they will lead a tour of five fish ladders in eastern Connecticut. Included on the tour will be the fish lift at Norwich Public Utilities' Greeneville Dam, which so far this spring has passed 160 shad, 780 alewife and one striped bass, according to Jeanne Kurasz, programs coordinator for NPU. While the runs on the other four fish ladders are over for the spring, visitors are likely to see fish Saturday at the Greeneville site, Gephard said.

The new ladder at Rogers Lake will also be on the tour. Built as part of a $330,000 project to restore the concrete dam at the lake, it opened in time for the annual spring migration of river herring - the collective term for alewives and blueback herring - into freshwater streams, lakes and ponds to spawn, after spending the winter hundreds of miles away in marine waters. The project was the result of a partnership between the town, DEEP and the Connecticut River Watershed Council, paid for mainly with federal, state and private grants.

No river herring swam up the Mill River through the new ladder this spring during the migration weeks - a result, Gephard believes, of a lackluster year for river herring returning through two fishways on the Mill River below the Rogers Lake ladder. The herring that did come through, he said, probably found plenty of spawning habitat in Lower Mill Pond and Mill Pond, but in a future year with a strong run, they'll find their way up the new ladder to Rogers Lake. The lake was one of the many historic spawning areas blocked off by dams built first by European colonists and then by successive generations that are now being reopened with dam removal and fish ladder projects.

"We did a lot of damage, and now it's time we brought back nature where we can," said Bonnie Reemsnyder, Old Lyme first selectwoman, on a visit to the fish ladder Thursday.

Harold said the conservancy's next projects in southeastern Connecticut will be construction of a fish ladder in Essex at Falls River, a tributary of the Connecticut River, and the removal of the Norton Paper Mill dam on the Jeremy River in Colchester. The conservancy is also seeking funds and permits for the removal of the Ed Bill's Pond dam in Lyme on the Eightmile River, and hopes to undertake that project in the summer of 2015, she said.

While Connecticut may not be host to the more dramatic fish migrations, such as salmon in the Pacific Northwest and sturgeon in the Danube River, the alewife, blueback herring and shad that journey up the state's rivers and streams to spawn are key components of the natural ecosystem, Gephard said. The runs have diminished but can be restored, he said.

"These are the great migrations we're trying to bring back," he said.

j.benson@theday.com

Local events on May 24 for World Fish Migration Day

• Talk about biology of migratory fish and conservation efforts, with Steve Gephard, head of the DEEP's Inland Fisheries Division, and Sally Harold, director of river restoration and fish passage with The Nature Conservancy, 9 to 11 a.m., Lyme-Old Lyme High School, 69 Lyme St., Old Lyme. After the talk, Gephard and Harold will lead tours of five fishways: Mary Steube and Rogers Lake in Old Lyme; Latimer Brook in East Lyme; Greeneville in Norwich; and Hallville in Preston. Registration required; parking is limited. To register, visit http://www.nature.org/ourinitiatives/regions/northamerica/unitedstates/connecticut/events/ct-world-fish-migration-day.xml.

• Open House at Leesville Dam Fishway on the Salmon River, 60 Powerhouse Road, East Haddam, 10 a.m. to 3 p.m. For more information, call (860) 447-4316. DEEP is hosting.

• Open House at Mary Steube Fishway on Mill Brook, in Griswold Nature Preserve near 25 Boston Post Road and Stoneleigh Road, Old Lyme, noon to 3 p.m. Old Lyme Land Trust is hosting.

• Open House at Rogers Lake Fishway on Mill Brook, 180 Boston Post Road, Old Lyme, 12:45 to 3 p.m. Town of Old Lyme hosting. For more information, call (860) 434-1605 ext. 212.

• Open House at Latimer Brook Fishway on Latimer Brook, near 80 Boston Post Road, East Lyme, 10 a.m. to 3 p.m. Hosted by DEEP's Inland Fisheries Division. For information, call (860) 447-4316.

• Tours of Greeneville Dam Fishlift and hydropower station on the Shetucket River, 5 Eighth St., Norwich, 10 to 11 a.m. Hosted by the city of Norwich and Norwich Public Utilities. For more information, contact Jeanne Kurasz at (860) 823-4182 or at JeanneKurasz@npumail.com.

• Open House at Hallville Pond Dam Fishway on Poquetanuck Brook, 40 Hallville-Poquetanuck Road, Preston, 12:30 to 3:30 p.m. Hosted by Eastern Connecticut Conservation District. For more information, call (860) 887-4163 ext. 403.

• For more information on other events in Connecticut and around the world for World Fish Migration Day, visit www.worldfishmigrationday.com.