The Tartar Strait was a puzzle to European explorers since, when approached from the south, it becomes increasingly shallow and looks like the head of a bay. In 1787 La Perouse decided not to risk it and turned south even though locals had told him that Sakhalin was an island. In 1797 William Broughton also decided that the Gulf of Tartary was a bay and turned south. In 1805 Adam Johann von Krusenstern failed to penetrate the strait from the north. Mamiya Rinzō's journey of 1808 was little known to Europeans. Gennady Nevelskoy passed the strait from the north in 1848. The Russians kept this a secret and used it to evade a British fleet during the Crimean War.