EXCLUSIVE: Investigation into protecting the city's water supply

NEW YORK (WABC) -- The terrorist group known as ISIS has shown a strong interest in dams. For a time, they had control over Iraq's largest until US air strikes got it back. Now, some experts say these events should be a wake-up call to tighten security of dams here at home.

"The dam infrastructure is a soft target, it's expansive and because of that it has to be close to the top of the list of targetable assets here at home," said Jeff Bernstein, a security expert.

Since 9/11, New York City has spent millions to better secure its 2,000 square mile watershed. The Department of Environmental Protection has hired more police. They've banned vehicle traffic on all dams and installed fencing and surveillance cameras at critical reservoirs.

"To look at potential vulnerabilities, we've done that and we continue to do that. And we employ measures to ensure the security of all our infrastructure," said Paul Rush, the NYC DEP Deputy Commissioner.

But has the city done enough? DEP sources tell Eyewitness News the police force is spread too thin as their numbers recently dropped below 200. The problem is one we reported on in the past: officers keep leaving for better paying departments, like the NYPD. Eyewitness News is also told, DEP is often slow to install security technologies. Pictures Eyewitness News has obtained show security camera poles at a major dam still without cameras even though they were installed five years ago. Adding to the concern is the location of many of the dams right in the center of public park lands.

"These critical assets are easily accessible by the public and because of that they are wildly exposed," said Jeff Bernstein, a security expert.

Jeff Bernstein who has worked with TSA and FEMA to secure critical infrastructure says New York City's water supply like most cities in America was built before the age of terrorism.

"They were made to hold water, they weren't made to withstand bomb blasts," Bernstein said.

DEP says it will not get into specifics about security but that they've spent at least a $100 million strengthening their dams. Their thousands of employees, many whom work out in the field, the agency says are the eyes and ears ready to detect the suspicious, the same goes for those who visit the dams.

"We have people fishing on our reservoirs, boating, who know the reservoirs inside and out," Rush said. "That access increases eyes and ears on the system."

"Do you sleep well at night?" Eyewitness News Investigative Reporter Jim Hoffer asked.

"I sleep very well at night," Rush said.