Richie, I assume that at this time people didn't yet realize that humans and animals (dogs) could be contaminated with Weil's disease (leptospirosis) by swimming in open waters in which rats live. Regardless of whether or not rats have been in this idyllic water, am I curious why 'Rover' was ordered to come out of the water. The answer doesn't really matter. However, the scene provides us with a precious 'action shot' from a past era.