Flooding in Wanaque, New Jersey: the record, the reservoir, and what to do
Wanaque is the town with the reservoir, and most questions about flooding here come back to Raymond Dam. The record shows the river below the dam does flood, but most of Wanaque's own claims come from the brooks running off the hills.
FEMA records 51 flood insurance claims in Wanaque. The Wanaque River below the reservoir has a long flood record of its own, 52 floods at the National Weather Service gauge between 1920 and 2018 plus newer crests in 2023 and 2024, but the stage-by-stage impacts the NWS publishes mostly fall downstream in Pompton Lakes. Inside Wanaque, FEMA names Post Brook, Meadow Brook and High Mountain Brook as the main flood sources. This page explains what the reservoir does and does not do, and what that means for owners and renters.
The short version
- FEMA records 51 flood insurance claims in Wanaque and eight repetitive-loss properties as of August 2026.
- The National Weather Service counts 52 floods on the Wanaque River below Raymond Dam between 1920 and 2018; the record crest is 10.82 feet in April 1984.
- The NWS says a reservoir spill does not cause flooding below the dam; FEMA models the reservoir as full when a storm begins.
- In Wanaque, Back Beach Park begins to flood at 7 feet and 4th Avenue takes on water at 9 feet, according to the NWS.
- FEMA names Post Brook, Meadow Brook and High Mountain Brook as Wanaque's main local flood sources.
Wanaque in the flood record
The US Census Bureau counts 11,206 residents in 4,450 homes in Wanaque, with a median year built of 1963 and about 21.9 per cent of households renting (American Community Survey, 2020–2024). FEMA flood insurance data list 51 National Flood Insurance Program claims in the borough over the life of the programme. The busiest years were 2011 with 10 claims, 2005 with nine and 1999 with eight; 2023 produced three. By named event, FEMA records eight claims from Hurricane Floyd, eight it labels torrential rain, seven from Hurricane Irene and three from a December nor'easter. As of August 2, 2026, FEMA lists eight Wanaque properties as repetitive-loss properties, one of them in the severe repetitive-loss category. The totals are small, but they show that a few addresses flood again and again.
The reservoir and the river below it
The Wanaque Reservoir is held back by Raymond Dam, and the river gauge just below it, the Wanaque River at Wanaque, has the same 90.4-square-mile drainage area as the reservoir gauge, according to the US Geological Survey. The National Weather Service counts 52 floods there between 1920 and 2018, and marks the flows as affected by regulation or diversion, which is what you would expect below a water supply dam. Flood stage is 6 feet, moderate 8 and major 9. The highest crests are 10.82 feet on April 5, 1984, 9.12 feet in March 1951, 8.42 feet in May 1968, 8.03 feet on March 11, 2011 and 7.88 feet during Irene on August 29, 2011. The river reached 6.02 feet on December 28, 2023 and 7.49 feet on January 10, 2024, the highest reading there since 2011.
What a reservoir spill means
Many residents assume that when the reservoir spills, the town floods. The National Weather Service addresses this directly in its notes for the reservoir gauge: spilling begins when the pool reaches 302.4 feet, it is a controlled release through the spillway when the reservoir is at or near capacity, it can go on for weeks or months, and it does not cause flooding below the dam. What matters for flooding is how full the reservoir is when a big storm arrives: FEMA's Flood Insurance Study models the reservoir as full at the start of a storm, the case in which it has no room left to store runoff. The study also gives a historical example. In May 1968 the borough flooded, damaging streets, homes, businesses and the Haskell sewage treatment plant, and USGS records indicated the flood would have sent the equivalent of a 20-year flow over Raymond Dam had the reservoir not been below capacity at the time. FEMA's study also states that dams in Passaic County are not managed as flood protection structures.
What the gauge means in Wanaque
Most of the National Weather Service impact statements for this gauge describe Pompton Lakes, downstream, where the Wanaque joins the Pequannock. In Wanaque itself, the NWS says Back Beach Park begins to flood at 7 feet and its athletic fields flood at 8 feet. At 9 feet, major flood stage, Back Beach Park is completely submerged and 4th Avenue in Wanaque takes on water. At 10 feet, homes downstream in Pompton Lakes flood, mainly in basements, and at 11 feet first-floor flooding occurs there. Only the 1984 and 1951 crests reached 9 feet. On the NWS's own list, the Wanaque impacts are parkland and 4th Avenue; the house flooding it describes is in Pompton Lakes.
The brooks that do most of the damage
FEMA's Flood Insurance Study says Wanaque experiences additional flooding from Post Brook, Meadow Brook and High Mountain Brook, generally in low-lying areas along these streams. FEMA estimated their flows with a regional method because they are ungauged, and it also mapped Rainbow Valley Lake and branches of Post Brook. The borough's mitigation list in the 2010 county plan, reproduced by FEMA, shows where officials saw the problem: dredging, deepening and widening Post Brook and its tributary, upgrading stormwater culverts, floodproofing identified flood-prone properties, and determining which properties are at risk if Monksville Dam or Raymond Dam were to fail. The study does not say which actions are complete.
What this means if you own or rent here
Look up the address on the FEMA Flood Map Service Center; there is no verified borough-wide flood-zone figure. If you are near Post Brook, Meadow Brook, High Mountain Brook, Back Beach Park or 4th Avenue, keep the basement floor clear and know the 7-foot and 9-foot marks on the Wanaque gauge. A news report of the reservoir spilling is not, on its own, a flood warning; a flood watch or warning from the National Weather Service is. Flood is a separate policy from homeowners or renters insurance, and FEMA states that a new flood policy normally takes 30 days to take effect. Whether a particular loss is covered is decided by your insurer and your policy. Never drive into water over a road.
Common questions
Does Wanaque, NJ flood?
In places. FEMA records 51 flood insurance claims and eight repetitive-loss properties in the borough. FEMA names Post Brook, Meadow Brook and High Mountain Brook as the main local sources, and the Wanaque River below Raymond Dam floods Back Beach Park and, at major stage, 4th Avenue.
Does the Wanaque Reservoir cause flooding when it spills?
The National Weather Service says spilling, which starts when the reservoir reaches 302.4 feet, is a controlled release that can last weeks or months and does not cause flooding below the dam. FEMA's flood study treats a reservoir that is already full when heavy rain arrives as the case that matters.
Which gauge should Wanaque residents watch?
The Wanaque River at Wanaque, on the National Weather Service water prediction site. Flood stage is 6 feet, moderate 8 and major 9. The reservoir elevation gauge shows how close the reservoir is to full, the condition FEMA treats as the worst case when a storm arrives.
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