Low-Head Dams: The “Drowning Machines” Every Boater Should Know About
When venturing onto the water, one of the most underestimated and deadly hazards is the low-head dam. These seemingly innocuous structures pose a serious threat to both boaters and personal watercraft (PWC) operators. Frequently referred to as “drowning machines,” low-head dams are responsible for countless accidents and fatalities each year. They may not have the dramatic appearance of large, towering dams, but their hidden danger lies in the unseen forces they create beneath the water’s surface.
In this blog post, we’ll explore what makes low-head dams so dangerous, how to identify them, and essential safety tips for staying safe.
What Are Low-Head Dams?
Low-head dams are structures built across rivers or streams to control water flow, prevent flooding, or manage irrigation systems. Unlike large dams, which are easy to spot due to their imposing height, low-head dams are typically small and span the entire width of a river. The top of these dams may even rest just a few feet below the water’s surface, making them difficult to notice, especially for an inexperienced boater.
The risk comes from how water behaves as it flows over the dam. When water cascades over the dam, it creates a recirculating current or “backroller,” often referred to as the “boil.” This powerful current can trap both swimmers and vessels, making it almost impossible to escape.
Why Are Low-Head Dams Known as “Drowning Machines”?
The nickname “drowning machine” is disturbingly accurate and highlights the unique risks of low-head dams. Here’s why they are so dangerous:
- Unseen Hazards
From a distance, low-head dams may seem harmless because their physical structure is often small. However, the danger lies beneath the surface where currents are most powerful. On smaller rivers, the backroller often stays close to the dam; on larger rivers or during high water levels, this dangerous current may extend over 100 feet downstream.
- Powerful Currents
The recirculating current created by water flowing over the dam is extremely strong. Once caught in this current, a person or boat is trapped in a cycle of being pulled underwater and forced back to the surface repeatedly. Even a well-designed personal flotation device (PFD) may not guarantee safety, as it cannot overcome the relentless pull of the current.
- False Sense of Security
Because low-head dams appear unthreatening, many boat operators underestimate their danger. Their size and lack of dramatic visual cues often lead boaters to assume these structures are safe to cross or approach.
- Uniformity of Hazards
Low-head dams span the entire width of a river, leaving no bypass route for boaters unless they exit the water entirely. This characteristic makes them especially hazardous for anyone unfamiliar with the area or unable to spot the dam in time.
How to Identify Low-Head Dams
Spotting a low-head dam can be tricky, but it’s critical to learn how to recognize them to protect yourself and your passengers. Here are some tips to help identify these dangerous structures:
- Research Beforehand
Before heading out on any river or waterway, research the area thoroughly. Local maps, boating guides, or online resources can provide information about the presence of dams in your area.
- Watch for Warning Signs
Many areas with low-head dams have warning signs posted upstream. These signs may be located on the shore or marked with buoys. Never ignore these warnings.
- Look for Changes in Water Flow
If you notice a sudden smooth horizon line on the river or a difference in water flow, it could indicate the edge of a low-head dam. White, rapidly flowing water downstream of this horizon line may also be a giveaway.
- Consult Local Boaters
If you’re new to an area, ask local boaters, outfitters, or guides about potential hazards, including low-head dams.
Essential Safety Tips for Boaters Near Low-Head Dams
Awareness and precaution are your best defenses against the dangers of low-head dams. Here’s how to stay safe:
1. Avoid Them at All Costs
The safest way to deal with a low-head dam is to completely avoid it. If you know there’s a dam on a river you plan to travel, plan your trip so you can exit the river and portage your boat around the dam. Never try to cross or approach a low-head dam.
2. Stay Alert and Vigilant
Always scan the water ahead and pay attention to your surroundings. Spotting a low-head dam early gives you the time and space to avoid it safely.
3. Obey All Warning Signs
Signs, buoys, and barriers are often placed well upstream of low-head dams to alert boaters to their presence. Respect these warnings and take immediate action to steer clear when you see them.
4. Portage Properly
When avoiding a dam, dock or beach your boat well upstream. This ensures you’ll avoid getting caught in the backroller or boil. Carry your boat down the shore and relaunch it well downstream.
5. Educate Everyone On Board
Make sure all passengers understand the dangers of low-head dams and how to recognize them. Knowledge is a crucial part of staying safe.
6. Equip Yourself for Safety
Always wear a personal flotation device (PFD) and keep safety gear like a throw rope or whistle on hand. While these won’t guarantee your safety if you’re caught in a backroller, they’re essential tools for general boating safety.
7. Check Water Levels
High water levels can make low-head dams even more dangerous by hiding them completely or extending their backrollers further downstream. Always check water conditions before setting out.
What to Do in an Emergency Near a Low-Head Dam
If you or someone else is trapped near a low-head dam, it’s critical to act quickly but safely:
- Avoid Attempting a Rescue from the Water
Entering the water to help someone trapped in a backroller is extremely dangerous and could result in multiple fatalities. Instead, use a throw rope or other long-distance rescue equipment to assist victims from a safe distance.
- Call for Help
Contact emergency services immediately if a rescue is needed.
- Warn Others
If you notice that others are approaching the dam unaware of the danger, signal to them to turn back.
Stay Smart, Stay Safe
Boating offers endless fun and adventure, but it also comes with responsibilities. Understanding the dangers of low-head dams is essential for keeping yourself and those with you safe on the water. Share this information with fellow boaters and make it a point to research and avoid these “drowning machines” during every outing.
By respecting the power of the water and incorporating strict safety practices, you can enjoy your time on the water while steering clear of unnecessary risks.