Girl cliff jumping in the boundary waters into water with a life jacket

Swimming in the Boundary Waters (Water Temperature, Depth, and Safety)

Swimming in the Boundary Waters is a wild, invigorating experience. With cool, clear, and clean water all around you, there’s nothing like a dip after a long day of paddling. The sun does a good job of warming the top few feet of water. But it’s not warm by any means. You’ll want to sprawl out on a nice, hot flat rock to warm up afterward like the turtles do.

However, these are wilderness lakes and so there are a few things to know before taking the plunge.

How cold are Boundary Waters lakes?

Of course, it depends on what time of year you venture into the BWCA. But if you go in July or August (the most popular months), you’ll find water in most lakes somewhere in the upper 60s degrees Fahrenheit. If you go earlier in June, water temperatures are bound to be a bit brisker – especially on bigger, deeper lakes. Smaller lakes are much quicker to warm up from the spring and summer sun, once ice is out.

Regardless, it’s no swimming pool (usually in the 80s degree Fahrenheit range). You’ll want to have something dry to change into when you’re done. Pro tip: warm-up on a nice, flat rock after a swim.

How deep are the lakes?

There are some very deep spots in the Boundary Waters. Several lakes have spots deeper than 200 feet and Lake Agnes (in Quetico) gets nearly 300 feet deep. But most of the paddling you’ll do in the Boundary Waters will be on about 10-30 feet of depth.

Read the map and the landscape

For swimming purposes, it’s wise to know where the dropoffs are around your swimming hole (particularly if you’re thinking you’d like to jump off a cliff!).

The first thing is to observe the water’s edge near your swimming hole. If there’s a steep cliff, chances are good that it keeps going down into the water, right? Whereas if the shoreline is a gently sloping beach area, it’s likely to be shallow at the water’s edge.

You can also consult your map to get a sense of water depth. The squiggly lines in the water represent water depth. Where they are closer together, the depth changes faster, and where they are more spread out the water is a more consistent depth. But the best way to get a good sense of depth is to paddle out to your swimming spot and drop a plumb line (or use a depth sensor/fish finder tool). If you can’t do that or don’t have the equipment, the next best thing is to simply swim as deep as you can. If it’s deeper than you can swim, it’s probably safe to jump into it (feet first of course). Which brings us to safety.

BWCA swimming safety

Swimming in the BWCA is not like swimming in the lake at the cabin, where you have the advantage of a car available, cell phone reception, and neighbors. The Boundary Waters is a wilderness area, and that means your safety is entirely in your own hands. If you slice your foot on a sharp rock, you will have to treat it yourself. Below are my four key swimming safety rules in the wilderness.

Always wear footwear (sandals or water shoes)

Your feet are too important in the wilderness to risk a preventable injury. For that reason, I always make sure people wear footwear in the water. I have seen too many lacerations on broken glass or sharp rocks in the water. You just don’t know what you might accidentally step on. And a cut on your foot is not only uncomfortable for the remainder of the trip, but opens you up to the risk of infection as well. So wear footwear in the water. I’m a fan of sandals that strap on your foot (like Tivas or Chacos). Others prefer a shoe that covers your toes as well – like a Keen Water Shoe.

Never dive head-first off cliffs

This one is obvious. The risk is just not worth it. Yeah, you may have grown up doing it or have seen others diving off the cliff on your lake, but past experiences do not predict future outcomes. Don’t do it. A head or neck injury in the BWCA is extremely serious and not worth the momentary thrill of a headfirst dive off a cliff.

Notice, I am not saying don’t jump off cliffs. That can be done with adequate risk analysis (like checking the water depth and for boulders in the water) but always, ALWAYS, jump feet first.

Don’t swim alone

Things can change fast on the water. Swimming alone – particularly long distances or in moving water – can be risky behavior. Especially for children or inexperienced swimmers, it’s a good idea to just never swim alone. Make sure there weaker swimmers are paired with stronger ones.

Consider floatation devices

In the wilderness, it is always better to overengineer safety. Since everyone is required to have a PFD or life jacket in the Boundary Waters, taking a swim is as good a time as any to put it to good use.


Swimming in the Boundary Waters is something everybody should experience. The cool, clean lakes of the wilderness make for a truly special memory. Just make sure you consider the particular risks of swimming in a very remote wilderness area. It is profoundly rewarding when done safely.