We’ve all seen at least one of numerous amateur video clips floating around the Internet in which a boater or fisherman captures a deer doggy-paddling its four little hooves off so far from shore it makes us gasp. Material like that is perfect fodder for the 6 o’clock news, allowing newscasters to lighten the mood between feature stories. Almost without fail, these tales typically end with commentary about how deer are phenomenal swimmers, often accompanied with guesstimates of the distances they’re capable of swimming. One such story claimed that deer can swim 8 to 10 miles. One video of some lobstermen rescuing a deer was allegedly filmed 5 miles off the Maine coast.
After watching one of these viral videos recently, I wondered: how far can deer actually swim, and has this ever been documented? As a biologist and employee of a science-based deer conservation organization, I felt it was our duty to “right the ship,” so I dove in by leveraging our relationship with the wildlife research community. I asked over 400 deer researchers for hard-hitting examples of GPS-collared deer crossing large expanses of open water. What I got back was surprising.
Soft Water, Hard Boundaries
Although we received some great illustrations of deer jumping in with both (sets of) feet to cross water without hesitation, one interesting finding that became immediately clear when I looked at the data was that the tendency to cross water is not equal for every deer. For some individuals even the smallest creek, crick or stream (or, whatever Grandpa called it) becomes the proverbial line in the sand for that particular deer, where his or her home range stops.
Case #1 – A 2022 Wisconsin study by Marie Gilbertson showed that landscape factors – including rivers, roads and general land-use like agriculture – influence deer dispersal, and impacts vary from the rate, distance and paths they choose to travel. Regarding crossing the largest water source in the area during a dispersal event, the majority of the 111 GPS-collared deer in the project chose not to cross the Wisconsin River, except a single adult doe (see the map below). The distance from shore-to-shore at the location where that doe crossed (northward arrow) is roughly 400 yards. This study helped shine a light on gene flow and potential disease transmission routes in the state.
Case #2 – University of Tennessee’s Kent Adams observed two of 12 collared adult does (points in red and green on the maps below) cross narrow tidal creeks at Chesapeake Farms in Maryland as part of one of the very first white-tailed deer GPS studies of our time (2003). This was discovered when Kent investigated habitat use related to crop depredation in an agricultural landscape, and the widest water crossing for the doe represented by red points is around 116 yards. But, that posed too great a swimming distance for the does displayed in blue, yellow and purple – at least during the project.
Deer Swim Open Water
I didn’t receive a ton of examples of collared deer that just so happened to get their Michael Phelps on across wide-open water, such as a lake or ocean, during a peer-reviewed study. This is likely because collars are expensive, so it’s rare to have a project with a large sample size and a lot of collars on deer to capture such movements. Moreover, it’s even more rare to find a study conducted right next to a large body of water. However, we did obtain a few.
Case #1 – The Minnesota Department of Natural Resources (DNR) shared an example of a lone GPS-collared fawn that crossed a moderate-sized lake as part of an ongoing study in their Farmland region. Now although the Land of 10,000 Lakes is well-known for its quantity and quality of big open water options, that fame certainly does not originate in the southwestern portion of the state, which is where the project is occurring. Tyler Obermoller, Ph.D. candidate and DNR Farmland biologist, told us that depending on whether the fawn crossed using the island as a pit stop or from shore-to-shore, the distance would be somewhere between 500 and 1,100 yards! This project aims to help managers better understand fawn survival rates, dispersal and habitat use in that area of Minnesota.
Case #2 – Paul Curtis with Cornell University provided two examples of VHF-collared/ear-tagged deer from my home state of New York. The first was during a 2011 white-tailed deer and tick study where researchers recorded two collared deer swimming from Shelter Island to the North Fork of Long Island. The shortest distance between the two points is roughly 1,000 yards of open water at the narrowest point. This amazed project coordinators not only for the distance traveled but also because of the deep, swift tidal currents at this location.
“A deer would definitely not be able to cross in a straight line!” Paul told me.
In the second example, an originally collared and ear-tagged deer from Fort Drum, New York, was eventually harvested by a hunter near Kingston, Ontario. That deer somehow made it across the St. Lawrence River, going from New York to Canada without a passport! Although researchers don’t know for certain where the deer crossed, the best guess is that it also swam just over 1,000 yards in order to cross the international border. The Ph.D. student on that project is currently finishing his dissertation and the results are not published yet.
Case #3 – In 1996 in California, U.S. Forest Service researcher Brian Boroski placed radio collars on more than 20 black-tailed deer living along the shorelines of Trinity Lake, a 25-square-mile reservoir at the headwaters of the Central Valley Project. Brian’s research was a precursor to a long-term study to assess California’s mule and black-tailed deer populations and habitat conditions on public lands. Although the herd of collared animals routinely crossed the large reservoir on a regular basis to satisfy their habitat needs – a distance of 500 to 700 yards – they did it so often Brian was able to develop and publish a specific technique for re-capturing them while they swam across!
Deer Swim Small Rivers
Generally speaking, deer spend a lot of time near flowing water. In many areas of the country, that is where you’ll find the best whitetail habitat and the majority of deer. Look to the Great Plains for a perfect example of this. Small rivers and large creeks are where watersheds eventually empty their contents, and the response from that periodic surge of moisture is a consistent supply of dense vegetation, which provides deer food and cover. Thus, a few cases of deer crossing a larger than average tributary was bound to surface from our query.
Case #1 – Dr. Duane Diefenbach of Pennsylvania State University (PSU) provided two examples where GPS-collared deer crossed the Allegheny and Susquehanna Rivers as part PSU’s groundbreaking Deer Forest Study. The Allegheny crossing was approximately 350 yards and the Susquehanna crossing was nearly 1,400 yards, with an island rest-stop on the way! Duane recounted this amazing journey in his PSU blog as that particular deer, a young female, was on a spring dispersal in Perry County that ended quite abruptly.
Case #2 – Brian Peterson with University of Nebraska-Kearney also responded to our request, not with GPS data, but with collected cast antlers! Brian scooped match sets from the same individual buck for three consecutive years as he aged from 3½ to 5½ years old, providing concrete evidence the buck had crossed the Platte River in central Nebraska. Brian found corresponding antlers at various distances from 700 to 1,700 yards apart. However, the buck’s straight-line channel crossing was an estimated 500 yards.
“It is not uncommon to see deer traverse the river daily, as many live on the woody sandbar islands, and many move primarily south daily to agricultural fields,” Brian told me.
The Platte River is a braided river that historically was a mile wide and a foot deep in areas, but woody encroachment over time resulted in permanent to semipermanent sandbars, so the river has become more channelized and deeper.
Deer Swim The Big River
By far the three longest documented cases of a water crossing during a peer-reviewed study came from different researchers and over 10 years apart, but from the same water source – the mighty Mississippi River. Beyond providing hard proof of how far a deer can swim, each of these examples gave unique insight into deer ecology, and they also fundamentally changed the way we think about our management and human influences on deer.
Case #1 – Researchers at Mississippi State University (MSU) Deer Lab collared a now famous deer, Buck #140, in the Mississippi Delta on December 20, 2020 about 5 miles from the banks of the Mississippi river. He left his capture location the following March when most of the land area was under water, swam the river and set up shop in Louisiana, 18 miles from his capture location. MSU graduate research assistant Luke Resop explained the river is about three quarters of a mile wide where the buck crossed, but it was at peak flood stage at the time, so Luke estimates he swam 1.25 miles (2,200 yards) during that movement! Buck #140 traveled back and forth over the next two years, crossing the river a total of four times.
Although Buck #140 was legally harvested by a Mississippi deer hunter in December 2022, MSU scientists said they still had something to learn from the deer.
“They had been hoping a hunter would kill the buck so it could be tested for Chronic Wasting Disease,” wrote Dac Collins of Outdoor Life. “They explained that since the buck [had] been wintering in a CWD management zone, a positive test would prove to wildlife managers that whitetails can spread CWD over long distances.”
The map below displays CWD locations in February 2022 right after Louisiana had announced their first CWD positive (yellow circle) in Tensas Parish. Since then, the Louisiana Department of Wildlife and Fisheries has detected 11 more cases in that area. Unfortunately, a reduction in requirements necessary to be covered under the Mississippi Department of Wildlife, Fisheries and Parks CWD Management Plan last summer removed four counties from that state’s CWD management area, including Claiborne County, which is directly across from Tensas Parish and just south of where Buck #140 lived. NDA strongly opposed this regulation change due to the risk it created.
Case #2 – In January 2007, wildlife ecologist and University of Arkansas professor Don White and his team began a GPS telemetry-based research project to define and evaluate factors influencing movements of free-ranging deer on the Freddie Black Choctaw Island Wildlife Management and Deer Research Area (WMA) in Desha County, Arkansas. The WMA is owned and managed by the Arkansas Game and Fish Commission (AGFC), and a primary goal of the study was to document deer movements and habitat use before, during, and after a flooding event. When they planned the study they didn’t know if the area would, in fact, flood. They got lucky: The study ran during several floods including a record-setting event in 2011. The researchers were able to follow 18 GPS-collared bucks when their normally dry home ranges went under nearly 40 feet of water for over a month.
The maps below show movements of four white-tailed bucks that crossed the Mississippi River from the WMA in southeast Arkansas on the west bank to private land in Mississippi on the east bank.
• Deer 79851 (red circles and line) was a 1½-year-old buck that left Arkansas on May 2, 2011, and later that day was located in Mississippi. This young buck swam 0.9 miles (1,600 yards).
• Deer 79863 (yellow) was a 2½-year buck that swam the river over a two-day period, and the greatest distance covered during one crossing event was 0.8 miles (1,400 yards). That buck eventually swam back to Arkansas nearly three weeks later, covering 1.9 miles, or over 3,300 yards.
• Deer 79847 (green) was a 2½-year buck that was swam 1.4 miles to Mississippi within two hours of being released. He returned to Arkansas seven months later, swimming 1 mile.
• Deer 79843 (orange) was a 2½-year buck that left Arkansas on May 5th, 2011, and later that day also made it to Mississippi in one paddle. The minimum linear distance this deer would have to swim to cross the river to get to Mississippi that day was 2.4 miles (4,300 yards) in a single shot!
This is the longest documented distance provided by any researcher. When I asked Don what he thought about these efforts, he said, “White-tailed deer are world-class athletes.”
I couldn’t have said it better myself.
How far can a deer swim? Thanks to the researchers who provided data for this article, we know of documented distances up to 2.4 miles. While this is shorter than some of the longer-range estimates reported on your evening news, I believe the verified crossings should be viewed as a minimum distance of deer swimming ability. Deer have an enormous set of lungs and what seems like endless stamina. I’d be willing to say many of those unsubstantiated claims may, in fact, hold water.