Like most tropical rainforest environments, Mamori Lake is home to a large number of wildlife species, some of which might be hazardous. Both piranhas and crocodiles are abundant in the waters of Mamori. However, like all wild creatures, they do not attack humans unless they are badly disturbed. As is common in the whole Amazon basin, there are poisonous snakes in the area, but they are very rarely seen or encountered. Insect bites are more a daily thing one gets used to live with than a real danger. Although not abundant, there is malaria in the Mamori region, and thus medical prophylaxis and prevention against mosquito bites are important and recommended. Brazilian health authorities also recommend proper vaccination for hepatitis, yellow fever and typhus. They might ask foreigners for an international vaccination certificate upon arrival at Manaus airport, depending on origin. Check with your airline if that is needed.