The Columbia River is swimmable in many spots, but it carries real risks that vary by location, season, and recent weather. Strong currents, cold water temperatures, bacterial contamination after storms, and toxic algae blooms all affect safety at different times. Knowing where and when to go makes the difference between a safe swim and a dangerous one.
Currents and Drowning Risk
The Columbia River’s most serious danger isn’t what’s in the water. It’s how the water moves. Currents shift depending on the tide, river level, and wind, which means a spot that felt calm last week can pull hard today. The river is wide and deep in many sections, and even strong swimmers can be caught off guard by underwater currents that aren’t visible from the surface.
Some locations are particularly dangerous. Portland Parks and Recreation specifically recommends against swimming at Kelley Point Park, where the Willamette River meets the Columbia, because of numerous drownings over the past decades. The western edge of the park is the most dangerous stretch. Confluence points like this create unpredictable currents as two rivers merge, and the bottom drops off steeply in places.
Cold water is the other physical hazard. Even in summer, the Columbia runs cold enough to cause gasping and muscle cramping if you jump in without acclimating. Cold water shock can incapacitate a swimmer within minutes, and hypothermia sets in faster than most people expect. Wearing a life jacket is genuinely important here, not just a suggestion for kids. Most river drowning victims were not wearing one.
Bacterial Contamination After Storms
Heavy rain flushes bacteria into the river through stormwater runoff, and in Portland, through occasional combined sewer overflows. Portland’s sewer system combines stormwater and sewage in some older sections of the city, and during heavy rain, the system can overflow directly into the Willamette River and Columbia Slough. These overflows happen roughly four times per rainy season, typically between October and May. The discharge is about 80 percent stormwater and 20 percent sewage, carrying E. coli and other bacteria at levels that can make you sick.
After one of these overflow events, the city advises staying out of the water for at least 48 hours. That same 48-hour rule is a good guideline after any heavy rainfall, even outside Portland, since agricultural runoff, pet waste, and other contamination washes into the river from communities along its entire length. Summer months with less rainfall generally mean lower bacterial levels, which is one reason swimming season and dry weather tend to overlap.
Toxic Algae Blooms
Cyanobacteria, often called blue-green algae, can produce toxins that cause skin rashes, nausea, vomiting, and in severe cases, liver damage. These blooms tend to appear in warmer, slower-moving sections of the river during summer and early fall, exactly when people want to swim. Shallow backwater areas and sloughs are more prone to blooms than the main channel, where faster-moving water makes it harder for algae to accumulate.
Oregon Health Authority issues advisories when cyanotoxins, particularly microcystin, are confirmed at unsafe levels through water testing. When a bloom is spotted, the water is typically sampled within one business day. If testing isn’t available quickly, a precautionary notice goes up instead. You can check current advisories on the Oregon Health Authority website before heading out. Blooms often look like green paint or thick scum on the water’s surface, and if the water looks discolored or smells off, stay out regardless of whether an official advisory has been posted.
Where People Swim Safely
Designated swimming beaches and popular swimming holes along the Columbia exist for a reason. These tend to be areas with calmer water, gradual entry points, and fewer hazards. Sandy River Delta, Rooster Rock State Park, and some stretches near the Columbia Gorge are popular spots where people regularly swim in summer. Look for areas with sandy or gravelly bottoms where you can wade in gradually and gauge the current before committing to deeper water.
Avoid swimming near boat ramps, shipping channels, or anywhere with heavy boat traffic. The wakes from large vessels can knock a swimmer underwater, and visibility is poor enough that boat operators may not see you. River confluences, bridge pilings, and areas near dams are also high-risk zones where currents behave unpredictably.
Practical Safety Steps
- Check conditions before you go. Look up current algae advisories, recent weather, and river levels. A few days of dry weather in summer is the best window.
- Wear a life jacket. River currents are not pool currents. Even experienced swimmers drown in moving water.
- Wade in slowly. Test the current at ankle and knee depth before going deeper. If you feel a pull, move to a different spot.
- Avoid swallowing the water. Even when conditions look good, river water carries bacteria and parasites that can cause gastrointestinal illness.
- Don’t swim alone. If something goes wrong in a river, having someone nearby who can call for help or throw a flotation device changes outcomes dramatically.
- Wait 48 hours after heavy rain. Bacterial contamination spikes after storms and takes a couple of days to flush through.
The Columbia River isn’t uniformly dangerous or uniformly safe. The people who enjoy it without incident tend to be the ones who pick their spots carefully, pay attention to conditions, and respect the fact that a big, cold river doesn’t forgive mistakes the way a swimming pool does.