Chucka Lassie : Season 16 Episode 22

Bob and his Navajo guide Sam find a dog swimming across Lake Powell on their way to survey tribal lands and rescue him; he is Chucka, an indolent dog who'd rather rest or play than tend sheep. But Chucka must ""grow up"" quickly after his shepherd owner, Charlie Ngani, is injured and Lassie must go for help.