Lake Geneva to swim at some beaches of the lake; indeed, visibility under water was near zero. By the 1980s, intense environmental pollution (eutrophication) had almost wiped out all the fish. Today, pollution levels have been dramatically cut back, and it is again considered safe to swim in the lake. Major leisure activities practiced include sailing, wind surfing, boating (including water skiing and wakeboarding), rowing, scuba diving and bathing. On a scientific footnote, in 1827, Lake Geneva was the site for the first measurement of the speed of sound in (fresh) water. French mathematician Jacques Charles François Sturm and Swiss Physicist Daniel
Geneva 15.7%. Of the agricultural land, 0.3% is used for growing crops. Of the water in the municipality, 0.2% is composed of lakes and 2.9% is rivers and streams. The altitude of Geneva is , and corresponds to the altitude of the largest of the Pierres du Niton, two large rocks emerging from the lake which date from the last ice age. This rock was chosen by General Guillaume Henri Dufour as the reference point for surveying in Switzerland. The second main river of Geneva is the Arve, which flows into the Rhône just west of the city centre. Mont Blanc