In 2009, on average 46% of Italian waterways were classified as class 1 (high) or class 2 and 81% were in classes 1 to 3. About 72% of lakes were in these three top classes (Figure 4.1). The number of bathing sites closed (i.e. sites where swimming was banned) during the summer season increased from 125 (2.6%) in 2002 to 310 (6.3%) in 2009, but it fell to 33 (0.7%) in 2010. Closing of these sites has been linked to toxic microalgae blooming, which occurs in many coastal regions.