Soon, I’ll be sharing a big story I’ve been working on, about the safety of the Adirondack Park’s most hazardous dams. The story focuses on hard-to-miss dams that have been closely monitored by state inspectors for decades. The dams likely pose the greatest public safety risk of any of the 500 Adirondack dams listed on the state’s dam inventory.
But many dams – or at least what remains of them – do not show up on any dam inventory, even as they fragment river ecosystems and threaten the migratory ability of numerous species.
These unmapped dams, known as “ghost dams,” certainly exist in the Adirondacks. A recent project led by The Nature Conservancy removed a small dam in Reber this summer to help extend important habitat for trout and salmon. The dam was not on the state’s inventory. Conservationists say there may be hundreds of such undocumented dams throughout the region.

An image from the study showing as dots unmapped dams in a sub-watershed of the lower Hudson River. The diamonds are dams listed on the state inventory.
A study of the lower Hudson River watershed (outside the Blue Line) published last year used remote sensing data to develop a method to estimate the location of undocumented dams. Focusing on Latinntown Creek and Foundry Brook sub-watersheds on either side of the Hudson near West Point, researchers discovered scores of untracked dams by analyzing water flow patterns and satellite images.
The researchers developed and tested a “machine-learning” model to predict the locations of unmapped dams. They projected that the state’s current dam inventory underestimated the true number of dams by between 80-94% in studied watersheds. They found that unmapped dams were distributed throughout the watershed and estimated an average dam density of one dam per 1,000 meters of stream.
“Many of the first anthropogenic barriers that an aquatic organism would encounter when migrating from the Hudson River estuary into either of the two study subbasins were unmapped dams,” according to the study.
Let’s hope these researchers find their way to the Adirondacks.
Photo at top: A small dam in Reber removed last year fragmented stream habitat even though it wasn’t registered on the state’s dam inventory, many hundreds like it may exist across the state. Photo by Zachary Matson.
This first appeared in Zach’s weekly “Water Line” newsletter. Click here to sign up.
I have been troubled by the presence of neglected and abandoned dams throughout New York ever since the Fort Ann incident many years ago. It is the elderly, now deemed useless dams on our secondary streams that are the most problematic. I am glad to learn some beginning steps are being taken to address at least some of these dangerous artifacts of our industrial and community past. If their breach or, better yet, removal will improve stream habitat, all the better.
This is really interesting. Great work.
Port Kent used to have a tiny dam on Watson Brook that was used to create an impoundment/reservoir to fill steam locomotive boilers for decades. 30+ years ago, a deluge on Trembleau Mtn. caused a flash flood that overfilled, then breached the little dam. The water rushing to Lake Champlain took out sections of several roads in its path, and completely washed the hillside and train station into the lake – leaving rails hanging in the air. It is entirely likely that if the dam had held, or was never installed, damage would have been much less.
There is good and bad to this story. Perhaps these majestic dams are not noticed on a map for a reason. It’s called nature and once published, it’s no longer nature. It’s in the UGLY hands on a controlling government. This is just a simplistic view from someone that is so grateful that these areas are kept QUIET for nature lovers.
Hey an idea take some of the $ from nonreliable solar and wind and repair and upgrade the small hydro dam’s in the DAK’s. They can fill in with Green Power when it is dark and no wind. Sadly thinking outside the box doesn’t fit the agenda/vision of money beggars/lobbyists in Albany or Washington