Which continent has no rivers that reach the sea year-round?

Australia, the driest inhabited continent. Most of its interior drains inward rather than to the coast, into salt pans that are dry almost all the time - Lake Eyre is the lowest point in the country and fills properly only a handful of times a century, at which point it becomes one of the largest lakes in the world for a few months and draws hundreds of thousands of waterbirds from across the continent.

The Murray-Darling is the major exception and is under enormous strain. It drains about a seventh of the continent, supports most of Australia's irrigated agriculture, and has repeatedly failed to reach the sea in drought years - the mouth has needed continuous dredging to stay open since 2002. Allocating its water between states, irrigators, towns and the river itself has been one of the longest-running political arguments in the country.

The variability is the defining feature rather than the average. Australian rainfall swings enormously between years with the El Nino cycle, so the continent alternates between drought and flood rather than settling anywhere - which is why European settlers, arriving in a wet stretch and applying English farming assumptions, made land management mistakes that took a century to recognise and are still being unpicked.