Complex sentence: In July, after living in the bus for three months, he decided to head back to civilization, but the trail was blocked by the swollen Teklanika River; the watercourse by that stage was considerably higher and swifter than when he'd crossed in April.
Split into simpler sentences: In July, after living in the bus for three months, he decided to head back to civilization, but the trail was blocked by the increased water level of the Teklanika River. The watercourse by that stage was considerably higher and swifter than when he crossed in April.