walking
Like many of the roads around the lake, the roads in Nesso are very narrow and frequented by full sized buses and apparently suicidal motorcyclists. Try not to walk on the road whenever possible. The beautiful cobbled walking paths either below or above the road provide an excellent alternative.
swimming
The water by Nesso certainly looks cleaner than the water near Como. However, one should exercise some caution when swimming in it as recent water quality reports have shown the waters of Lake Como to have 68 times the accepted level of colony-forming bacteria (http://www.thespec.com/Ne...). It is thought that this is from incomplete waste treatment.