Lesseps wanted a sea-level canal (like the Suez), but he visited the site only a few times, during the dry season which lasts only four months of the year.[15] His men were unprepared for the rainy season, during which the Chagres River, where the canal started, became a raging torrent, rising up to 10 m (33 ft). The dense jungle was alive with venomous snakes, insects, and spiders, but the worst challenges were yellow fever, malaria, and other tropical diseases, which killed thousands of workers; by 1884, the death rate was over 200 per month.[16] Public health measures were ineffective because the role of the mosquito as a disease vector was then unknown. Conditions were downplayed in France to avoid recruitment problems,[17] but the high mortality rate made it difficult to maintain an experienced workforce.