A few days ago we visited the Damariscotta Mills Fish Ladder Restoration in Newcastle, Maine. Some online investigation (very incomplete) turned up interesting information. The Damariscotta Fish ladder was built around the mills in 1807, and reconsted two centuries later between 2007 and 2017. As reported by GMG, construction at the smaller West Gloucester Alewife/Herring fish ladder on Little River, allowing spawning above in Lily Pond, was completed in 2018. It appears SumCO eco contractors and/or Becker Construction had a hand in both projects (need clarification).
Here are some photos from our Damariscotta Fish Ladder visit. The site was not staffed, and access was limited. Their website is: damarascottamills.org