Swift, moving water is one of the most overlooked but lethal hazards hikers can encounter in the mountains. Recent tragic accidents in the local San Gabriel Mountains highlight these risks, and SAR teams hope to prevent future tragedies by increasing public awareness. The following discussion outlines the hazards presented by moving water and how hikers can better assess and manage those risks.
Objective Hazards of Moving Water
Moving water presents many objective hazards that we cannot control and are often unfamiliar with as casual hikers in the mountains. Some of these include:
– Hydraulic force of water: Even water at knee–thigh depth can knock an adult over if it is moving quickly; the force increases dramatically with depth and speed.
– Strainers and entrapment: So-called “strainers” such as logs, branches, brush, and boulder sieves allow water to pass through but can trap a person, holding them underwater.
– Foot entrapment: A foot wedged between rocks or under wood in swift current can pin a person face-down, leading to drowning. People swept off their feet often attempt to stand up and can get a foot caught.
– Waterfalls, drops, low head dams, and undercut banks: Rapids, falls, and undercut banks can flush a swimmer into hydraulics, recirculating holes, or pockets where escape is difficult. Low head dams that cut across a river from bank to bank can create extremely dangerous hydraulic “holes” immediately below the dam.
– Cold shock and hypothermia: Snowmelt or very cold water can cause cold shock, gasping, loss of coordination, and rapid hypothermia, impairing self-rescue or creating a serious situation if someone cannot quickly get warm and dry.
– Debris and poor visibility: Murky or surging water may carry branches and conceal rocks or other hazards.
– Backpack and gear hazards: A loaded pack can push you off balance, hold you underwater, or snag on obstacles unless it can be quickly ditched.
– Dynamic conditions: Heavy rain, snowmelt, and dam releases can change a seemingly safe crossing into a dangerous one within hours. Late-day crossings may be especially hazardous due to snowmelt increasing water levels.
Subjective Hazards, Risk Assessment and Decision Making
While we cannot control objective hazards, we can control subjective hazards. The most important decision skill when encountering moving water is recognizing when not to cross and choosing to turn around, wait, or find another route.
Key assessment steps used by organizations such as the Pacific Crest Trail Association, state wildlife agencies, hiking groups, and search and rescue teams include:
– Consider depth and speed: Water above mid-thigh or moving faster than you can comfortably walk is likely too dangerous to cross on foot.
– A simple field check involves throwing a stick in the current. If it moves faster than your normal walking pace, the crossing is likely unsafe.
– Consider downstream hazards and “runout”: Identify what happens if you fall and are swept downstream. Look for strainers, boulder gardens, rapids, dams, falls, or undercut banks.
– A safer crossing has an open, obstacle-free runout where a swimmer could exit the water.
– Choose location carefully: Prefer wide, shallow sections with firm bottoms and good entry and exit banks.
– Avoid narrow constrictions, obvious rapids, or crossing immediately above logjams, strainers, waterfalls, or dams.
– Environmental and human factors: Consider recent rain, snowmelt, air and water temperature, group fatigue, group experience, pack weight, swimming ability, and physical limitations within the group.
– Be cautious of decision-making shortcuts or heuristics. Just because someone crossed recently or you crossed safely before does not mean conditions are safe now.
– Be conservative. If conditions appear marginal, find an alternate route, wait for levels to drop, or turn around.
A simple mental model is useful: If any one of depth, speed, or downstream hazards is high, treat it as a no-go; if two are concerning, you should already have decided not to cross.
Ropes and Why Tying In Is Dangerous
Guidance from trail organizations, the PCT community, and swiftwater rescue instructors is remarkably consistent: do not tie yourself or others to a rope in moving water unless you have professional-level swiftwater training and equipment.
Risks associated with tying into a rope include:
– Being pinned underwater: A rope anchored to shore can pull a fallen hiker into rocks or strainers and keep their head submerged.
– Strangulation and entanglement: Loose rope can cinch around limbs or neck and prevent swimming or self-rescue.
– Dragging others down: Tying multiple people together means one fall can pull an entire group into the current.
– Creating an in-water hazard: A rope stretched across current becomes another strainer capable of trapping swimmers.
What Can You Do to Cross Safely?
A variety of techniques are commonly taught by trail and hiking organizations and are described in resources such as Mountaineering: Freedom of the Hills. These approaches align with widely accepted backcountry safety practices.
Preparation and equipment
– Keep boots or shoes on for traction and foot protection; avoid crossing barefoot.
– Loosen or unclip hip belts and sternum straps so your pack can be quickly ditched if you fall.
– Use trekking poles or a sturdy stick to provide additional points of contact and to probe depth or unstable footing.
– Secure loose items and stow dangling straps or clothing that could snag.
– Ensure everyone understands the crossing plan and what to do if someone is swept off their feet.
Solo crossing technique
– Face upstream, lean slightly into the current, and cross at a shallow angle, often slightly downstream.
– Take small shuffling steps while maintaining at least two points of contact at all times.
– Probe ahead for holes, unstable rocks, or drop-offs before committing your weight.
Group crossing techniques
– Line or wedge formation: Stand side-by-side with the strongest or tallest person upstream to break the current. Move together and communicate each step.
– Tripod or triangle stance: Three people form a triangle facing inward, leaning against each other for support, and shuffle together slowly.
In all cases, the no-rope tie-in rule applies, and these methods should only be attempted at crossings that clearly fall within conservative safety limits.
If You Are Swept Off Your Feet
Swiftwater safety guidance commonly teaches a “defensive swimming” position:
– Immediately ditch your pack or any gear that could hold you underwater.
– Float on your back with your feet pointed downstream and your head upstream so you can see hazards.
– Keep your feet up to protect against rocks and obstacles.
– Avoid attempting to stand until you reach slower, shallower water.
– Move with the current toward the nearest safe shore or eddy.
– Once out of the water, focus on getting warm, drying off, and assessing injuries.
– Consider contacting SAR if injuries occur or if recrossing the water would be required.
Decision Frameworks and Pitfalls
The most important tool we have in managing risk is our judgment. Everyone is susceptible to decision-making shortcuts that can obscure real hazards.
No-Go Criteria
– Water above mid-thigh, especially with strong current.
– Current faster than a comfortable walking pace.
– Dangerous downstream hazards such as strainers, waterfalls, or boulder sieves.
– No safe exit point on the opposite bank.
– Fatigue, cold, solo travel, or poor swimming ability.
Safer-Side Criteria
– Wide braided channel with water below the knee and moderate current.
– Clear visibility of upstream and downstream hazards.
– Strong group communication and an agreed emergency plan.
If conditions do not clearly fall within the safer-side criteria, the conservative choice is to delay, reroute, or turn back.
None of the above is intended to provide detailed training. Hands-on instruction and practice are invaluable when learning how to evaluate and safely manage swiftwater hazards.
References
– Appalachian Trail Conservancy – https://appalachiantrail.org/experience/hike-the-trail/essential-skills/safety/weather-hazards/river-stream-crossings/
– Pacific Crest Trail Association – https://www.pcta.org/discover-the-trail/backcountry-basics/water/stream-crossing-safety/
– Green Mountain Club – https://www.greenmountainclub.org/education/hiking-101-vermont/safe-water-crossing/
– Wilderness Medical Society – https://wms.org/magazine/magazine/1263/Creek-and-River-Crossings/default.aspx
– Rocky Mountain National Park – https://www.nps.gov/romo/planyourvisit/swift-water-safety.htm
– Mountaineering: Freedom of the Hills – https://www.mountaineers.org/books/books/mountaineering-the-freedom-of-the-hills-10th-edition
– Sierra Madre Search and Rescue – https://smsr.org/2026/01/04/heuristics-risk-and-decision-making/
– River Rescue – https://www.nrs.com/river-rescue-4th-edition-book/pu3d