UPPER DELAWARE REGION—The Delaware River has a broad reach.

It’s the largest undammed river east of the Mississippi, and over 13 million people rely on its water for drinking. Tourists and fishers flock to it when the weather is good, injecting life into the region’s economy and culture. Those who live along its banks face flooding that damages homes and infrastructure when storms visit the region.

The regional ecosystem attached to the river was bracing for a major impact in the fall, preparing itself in anticipation of a major repair project on the Delaware Aqueduct. That ecosystem is now breathing a sigh of relief, since the project has been pushed back to October 2023.

The Delaware Aqueduct runs underground from the upper Delaware to the Hillview Reservoir on the outskirts of the Bronx. It’s the longest continuous tunnel in the world, measuring 87 miles in length.

The water that goes through it impacts communities at its destination and at its source. New York City and its environs consume around a billion gallons of water daily, and water from the aqueduct makes up about half that total.

It serves a different purpose for the communities along the Upper Delaware River. The 600 million gallons a day that the aqueduct takes to New York City come from four reservoirs at the head of the Delaware River: the Cannonsville, the Pepacton, the Neversink and the Rondout. By drawing water from those reservoirs, the Delaware Aqueduct helps keep them from overfilling and causing flooding further downriver.

The New York City Department of Environmental Protection (DEP) needs to shut down the aqueduct for five to eight months to repair a set of leaks near Newburgh and Wawarsing. This shutdown was originally planned to start in October of this year.

But closing the aqueduct has the potential to make flooding more likely along the Delaware River.

There’s always a management challenge with the reservoirs on the Upper Delaware River, said Jeff Skelding, executive director of the Friends of the Upper Delaware River (FUDR). Keeping the reservoirs fuller lets the DEP keep more water in reserve for the city. Keeping them emptier gives them more capacity to absorb stormwater before they start flooding.

To safely close the aqueduct, the DEP will need to draw down the reservoirs by enough that five to eight months’ worth of rainwater won’t cause them to overflow.

The DEP planned to draw down the Pepacton Reservoir to around 1255 feet, the Cannonsville Reservoir to around 1125 feet and the Neversink Reservoir to around 1415 feet prior to the shutdown. Water starts to spill over at each of the reservoirs at around 1280 feet, 1150 feet and 1440 feet respectively.

The plan didn’t fully assuage the fears of groups like FUDR, Trout Unlimited and the Upper Delaware Council (UDC).

Trout Unlimited and FUDR did their own independent analysis regarding the past 10 years of inflows. That analysis indicated that the DEP’s planned drawdown still ran the risk of flooding further along the river.

“Our analysis that even a 30 percent void might not inhibit the threat of problematic flooding in the communities below the dams,” said Skelding.

Answering this analysis wouldn’t be simple for the DEP. The Delaware River is a broad ecosystem, and a complex set of treaties and rules governs its management.

The Supreme Court issued a decree in 1954 allowing New York City to withdraw up to 800 million gallons a day from the Delaware River, on the condition that it release enough water from its Delaware River services to maintain 1750 cubic feet per second of river flow at Montague, NJ.

The 1954 decree still holds today, and is administered through a set of rules called the Flexible Flow Management Plan.

The releases the DEP would have to make to address the risk of flooding would break the rules of the FFMP. Trout Unlimited and FUDR have called upon the DEP to request an exemption from the FFMP for this reason, giving it a freer hand to manage flood risk along the Delaware River.

The DEP has requested exemptions from other treaties in the process of planning for the Delaware Aqueduct shutdown, but didn’t see it as necessary in case of the FFMP. The office of the Delaware River Master, the body that administers the 1954 decree and the FFMP, doesn’t see it as necessary either.

“NYC DEP has done analysis of scenarios relating to the shutdown, including a range of rain possibility and the subsequent impacts,” says Delaware River Master Kendra Russell. “The River Master’s office doesn’t foresee difficulty in meeting the requirements of the 1954 decree,  especially given they will be operating within the Flexible Flow Management Program.”

Even operating within the FFMP, the DEP’s shutdown plan will impact the region’s fish and those who catch them.

The reservoir releases will operate at their maximum capacity in the months before the shutdown to empty the reservoirs and prepare for what is to come.

For Evan Padua, a river guide who runs Sweetwater Guide Service with his father, flooding changes patterns of behavior for both fishers and fish. Fishers consolidate in the places on the river that are still suitable for fishing; fish start to avoid those areas.

And with different patterns of releases impacting what fish are in the river, that impact gets passed along to the fishers and the river guides who are making a living out on the river.

The DEP isn’t delaying the aqueduct project in consideration of its Delaware River impacts. It plans to go ahead in the fall of 2023, according to DEP spokesperson Edward Williams. “There are a few remaining projects that, while they are close to being completed, engineers want them to be completed, tested and staff fully trained well in advance of the shutdown.”

Those concerned about fishing and flooding along the Delaware River can breathe a sigh of relief until then. Come next summer, that sigh of relief will turn back into a breath of anticipation, as the ecosystem of the Delaware River prepares itself once again for impact.