evidence: FLOATING Sargassum IN SERRANILLA BANK, CARIBBEAN COLOMBIA, MAY JEOPARDIZE THE RACE TO THE OCEAN OF BABY SEA TURTLES [...] Serranilla Bank is an ancient atoll in the Caribbean Sea, at 15° 50' N and 79 ° 50' W (Fig. 1). It has several small cays emerging from the water to form some permanent islands. These oceanic cays, isolated from other emerged territories, have been recognized only recently as important nesting areas for sea turtles (Barrientos-Muñoz and Ramirez-Gallego, pers. comm.). In September 2017, the Colombian Commission for the Ocean (CCO), with the financial support of Colciencias and Dimar, and the logistic support of the Colombian Navy (Armada de Colombia), organized a scientific expedition (Seaflower Expedition 2017) to Serranilla bank, to study the biodiversity of this remote area of the country. During this expedition, we observed great amounts of floating Sargassum reaching the beaches of Beacon Cay, the largest island in Serranilla Bank (Fig. 2). The algae accumulated on the beaches, and formed a thick mat to 40 cm high. Along the beach, a great number of sea turtle nests were reported (Barrientos-Muñoz and Ramirez-Gallego, pers. comm.) which, by the time of the Sargassum wave, were ready to disclose.