In 1197, King Richard I sold the Crown's rights over the Thames to the Corporation of the City of London, which tried to issue licensing to boats on the river. It remained under royal prerogative until 1350 when King Edward III passed an Act of Parliament prohibiting the obstruction of the River. Structures that had been built out into the river for fishing and milling purposes made the river difficult to navigate and lent to it an unregulated chaotic mix of boats.