Simplify the following text for a Grade 3 native English-speaking person.
Original: On 22 October they found that the only way to pass the Murrumbidgee River , then in flood , was to convert one of the carts into a type of boat by passing a tarpaulin under it ; the men , horses , and bullocks swam over , and everything was successfully got across .
Simplified: The Murrumbidgee River was in flood so they had to make one of the carts into a kind of boat to get across . The men , horses , and bullocks swam over .