SOUTH NYACK, N.Y. (CBSNewYork) — The new Tappan Zee Bridge may be costing us more than originally thought.

Environmentalists are blaming the construction project for killing endangered fish in the Hudson River.

As CBS2’s Lou Young reported, its been around since pre-history, but some are wondering if the Atlantic Sturgeon has finally met its match where the new Tappan Zee Bridge is being built.

The animals, which live an average of 60 years and can grow up to 15 feet in length, spawn in the river and have been turning up dead in what the environmentalists at Riverkeeper say are alarming numbers.

“This is an endangered species. The last published study on Atlantic Sturgeon had a total of 860 mature sturgeon in the Hudson River population,” said Leah Rae, with Riverkeeper.

In all cases, motorboats are being blamed, but the fish float far from the scene of the impact so solving the case is not likely an episode of CSI, Young reported.

“Unfortunately, boat propellers don’t leave DNA on the fish that they’re killing, right? So what we’re looking at is the change in numbers of fish that are being killed since the project began,” said Dan Estrin, with Pace Law School.

According to data, there were six deaths between 2009 and 2011, eight in 2012, 25 in 2013 and 43 in 2014.

The Hudson is a big river with lots of boat traffic, but most of it happens out in the channel. But thousands of boat trips have been added in the shallows since the bridge project began, and since that’s where the sturgeon feed, that’s where the problem is, Young reported.

The bridge constructors said they’ve bent over backward to minimize environmental impact using bubble curtains to shield the sturgeon and are aggressively monitoring the endangered fish, even reporting some of the kills mentioned in the state reports.

A spokesman said they’re “Working with the appropriate state and federal agencies to look into the claims recently made by Riverkeeper.”

Riverkeeper is asking federal regulators to strictly enforce boat speed limits in the shallows and to review construction practices that could impact the endangered fish.