Simplify the following text for a Grade 9 native English-speaking person.
Original: In 1830 Captain Charles Sturt reached the river after traveling down its tributary the Murrumbidgee River and named it the Murray River in honor of the then British Secretary of State for War and the Colonies Sir George Murray , not realizing it was the same river that Hume and Hovell had encountered further upstream .
Simplified: Explorer Charles Sturt renamed the river in January 1830 after a British politician , Sir George Murray .