Deer infected with epizootic hemorrhagic disease (EHD) go to water because they are running dangerously high fevers and are severely dehydrated. Standing or lying in water is their only way to cool down, and the internal damage the virus causes makes them desperately thirsty. This is why dead deer during late-summer EHD outbreaks are so often found in or right next to ponds, streams, and creek beds.
Fever Drives Them to Cool Down
EHD triggers intense, sustained fever in infected deer. As the virus replicates and damages blood vessel walls, the immune response pushes body temperature high enough that the deer instinctively seeks relief. Water is the most effective cooling source available in the wild. Infected deer will wade into ponds, lie down in shallow streams, or stand in any water they can find, trying to bring their core temperature down. This behavior is so consistent that wildlife agencies use the sight of deer carcasses near water as one of the first field indicators of an EHD outbreak.
Internal Bleeding Causes Severe Dehydration
The “hemorrhagic” in EHD’s name describes what happens inside the deer’s body. The virus attacks the lining of blood vessels, causing widespread internal bleeding. In the acute form, this leads to bloody diarrhea, blood in the urine, and bloody discharge from the nasal cavity. All of that fluid loss creates extreme dehydration on top of the fever.
A deer losing blood and fluid internally becomes intensely thirsty. The combination of fever and dehydration creates a powerful, compulsive drive toward any available water source. Even deer that would normally avoid open areas or human structures will walk right up to backyard water features, livestock troughs, or roadside ditches. They lose their normal fear of humans entirely.
Swelling Makes Eating and Drinking Difficult
EHD also causes significant swelling, particularly of the head, neck, tongue, and eyelids. Ulcers can develop on the tongue and the dental pad (the hard tissue on the roof of a deer’s mouth). This swelling and tissue damage makes it painful or even impossible for the deer to eat normally, and it may interfere with swallowing water efficiently. So even when a deer reaches water, it may not be able to drink enough to offset the fluid it’s losing. This creates a cycle where the animal stays near the water source because its thirst is never fully satisfied.
How EHD Progresses
The disease moves fast. Early signs include loss of appetite and a deer that seems unusually unbothered by people. As the infection progresses, the deer salivates excessively, develops rapid breathing and a racing pulse, and grows visibly weaker. At this stage, most infected deer are already seeking water. In the acute form, the disease carries high mortality rates, especially in northern deer herds that have little preexisting immunity to the virus. Many deer that reach water never leave it. They become unconscious and die right where they were trying to cool off.
This is why hunters and landowners during late summer and early fall sometimes discover multiple deer carcasses clustered around a single pond or stream. It’s not that the water itself is dangerous. The deer all came to the same place for the same reason: fever and thirst brought them there, and the disease killed them before they could recover.
Why Outbreaks Cluster Near Water in Other Ways
There’s an additional layer to the connection between EHD and water. The virus is transmitted by biting midges (tiny flies sometimes called “no-see-ums”) that breed in mud along the edges of ponds, streams, and other slow or still water. During hot, dry summers when water sources shrink, deer concentrate around whatever water remains, and the midge populations thrive in the exposed muddy margins. This puts deer and the insects that carry the virus in exactly the same place at exactly the same time.
So water plays a role at every stage of EHD. It’s where the midges breed, where deer get bitten, and where sick deer return as the fever and dehydration take hold. The first hard frost of fall kills off the adult midge population and effectively ends transmission for the season, which is why EHD outbreaks are almost exclusively a late-summer and early-fall event.
What to Look For
If you find a dead deer near water between August and October, EHD is one of the most likely explanations, particularly if you find more than one. Look for a deer that appears swollen around the face or head, or one with visible discharge around the nose. The carcass may also show signs of having been in or very close to the water’s edge. Reporting suspected EHD deaths to your state wildlife agency helps biologists track outbreaks and understand how the virus is moving through local deer populations. Most states have an online reporting tool or a phone number specifically for wildlife disease reports.
EHD does not infect humans or pets, and it is not spread through contact with a dead deer. The virus requires the midge as an intermediary and cannot survive outside that transmission cycle.