Way too big for just 100 pounds.
And they're nowhere to be seen in the most recent Google aerial.
The spoils from dredging are pumped into similar "eco-friendly" containers. Could be. Our boat club voted that option down a few years ago - it was very expensive.
Dredging on that part of the river, with the intakes for the pumped energy storage facility, is probably mandatory.
The photo is of a little part of the reservoir up top, not the river.
Perhaps storage of dredging the reservoir impoundment.
Western Mass tourist attraction? The big sacks.
Oh, I'll bet they definitely need to keep the reservoir dredged.
Every time they pump it up, must bring muck up from the river that gradually fills the pond up. Now they have to find a way to get rid of it.
Interesting that when the pumped storage reservoir became operational during the early days of the EPA, it was the largest in the world! Wikipedia
has some info.