Have you ever been camping in the Boundary Waters and witnessed a person all lathered up with soap jump into the water? I cringe just thinking about seeing such a thing because I know even biodegradable soap contaminates the water.
In order for soap to biodegrade in the BWCA or anywhere it needs soil. That is why it is recommended to wash dishes and yourself 200 feet from the shoreline. Think about where your cooking and drinking water comes from when you're canoeing and camping in the Boundary Waters. This should encourage you to keep soapy water and other contaminates out of the lake.
If you wouldn't want to drink it then you shouldn't put it into the water. Think about how bad bug spray tastes on your lips and how Deet can eat clothing. Sunscreen, lotions and bug spray can end in the water if you go swimming without pre-washing yourself. Just get a few pots full of water and rinse off well away from the water before jumping into the crystal clear lakes of the Boundary Waters.
It would be nice to be able to not use soap or other contaminates while camping in the Boundary Waters. While this isn't real practical you can find some soaps that are better for the environment than others. Campsuds is a popular vegetable based cleaner that's been around since 1965. It is competely biodegradeable as is Dr. Bronner's Magic Soap and a variety of others you can find online.
Just remember, in order for any soap to biodegrade it needs soil so keep it out of the water and focus less on keeping your body clean and more on keeping the lakes of the BWCA drinking water clean.