Even if the label says 'biodegradable,' please don't do it.
I was lying on a hot sandy beach yesterday morning, looking at the turquoise waters of Lake Huron, when a man began lathering himself vigorously in the lake in front of us. He rubbed foamy shampoo all over his head and body, then dove into the water to rinse it off.
What this man clearly did not realize -- or perhaps chose to ignore -- is that washing oneself with soap of any kind in a lake, pond, river, or ocean is terrible for the environment. Even if the bottle is labeled biodegradable, natural, or organic, it's still bad. A so-called eco-friendly cleanser, while containing fewer noxious chemicals than a conventional brand, is still not meant to be poured directly into a waterway -- even if it has a green reputation like Dr. Bronner's or a name like Campsuds.
There are several reasons for this. The detergent in soaps breaks the surface tension of the water, something that we humans may not notice, but that's crucial for critters such as water striders to get around. Lower surface tension reduces the oxygen level in the water, causing harm to fish and other aquatic wildlife. Surfactants in soaps are toxic to lake life, particularly tiny invertebrates.
Phosphorus is a notoriously harmful ingredient, now less common than it was a few decades ago, but still known for feeding algae. In fact, soap in general boosts nitrogen levels and triggers algal growth, those unsightly blooms that cloud water's clarity and turn a lovely swimming spot into an icky one. From the Belgrade Regional Conservation Alliance,
"Soapy runoff is great food for algae — both silt and dirt and the chemicals in the soap are junk food for algal growth."
Part of the problem is the number of people now camping and cottaging in the forest. A single person's morning bath in a lake won't cause total destruction of the lake habitat overnight, but the cumulative effects of many people doing it cause problems over time. Advice columnist Umbra at Grist writes,
"According to the EPA, an ounce of biodegradable soap needs to be diluted in 20,000 ounces of water to be safe for fish. Now imagine all of your neighbors scrubbing down on their docks, and you can see how the health of your small lake could be significantly compromised."
A safer approach is to soap up at least 200 feet (61 meters) from shore. Fill a bucket with water and use it to wash and rinse at a distance from the lake. In fact, the popular camping soap Campsuds states clearly on its container, "Soap up and wash at least 200 feet away from alpine lakes and streams. Dig a hole 6 to 9 inches deep for disposing of soapy wash and rinse water. This allows bacteria in the soil to completely and safely biodegrade Campsuds."
This advice applies to any soap. The soil acts as a filter, helping to accelerate biodegradation and to protect wildlife by masking the smells of whatever you've been cleaning.
Another option is simply not to wash with soap while out in the bush. The physical act of scrubbing accounts for much of cleaning one's body, so jump in a lake and give yourself a good rubdown, sans soap. You'll emerge significantly cleaner.
Keep in mind that whatever products you have on your skin will be washed into the lake, as well. This is why Hawaii has recently banned chemical sunscreens; they're washing off swimmers in such enormous quantities that they've destroyed coral reefs. Try to avoid anti-perspirants, dry shampoos, lotions, and makeup if you plan to swim. Spare the aquatic wildlife the toxic runoff from your chemical-laden beauty routine and it may be there more years for you and your children to enjoy.