Hydrophis semperi, commonly known as the Lake Taal snake, Garman's sea snake, the Philippine freshwater sea snake, and the Luzon sea snake, is a rare species of venomous sea snake found only in a single lake on the island of Luzon in the Philippines. It is noted for being one of two known species of sea snakes that are known to be found almost-exclusively in freshwater. The other freshwater sea snake species is Laticauda crockeri.