Pavel Urysohn (1898-1924) was a Russian mathematician of Jewish origin who is best known for his contributions in dimension theory, and for developing Urysohn's Metrization Theorem and Urysohn's Lemma, both of which are fundamental results in topology.
Urysohn drowned while swimming in the sea, on vacation in France off the coast of Brittany, France, near Batz-sur-Mer, and is buried there. He was accompanied by his colleague and friend, Pavel Alexandrov (another famous mathematician). It is believed that Alexandrov was incredibly distressed by this tragedy, and deeply regretted his inability to save his friend.
MORAL OF THE STORY : Topologists should not go swimming.