At the end of each walk, we just shout bath to Brodie and he jumps into the reed water at the car park and splashes around till he gets all the mud off. Then we towel him and he jumps in the back or the car.
With Hamish, (who does not go swimming), he wears a very macho cotton t shirt and at the end of the walk we take it off and hey presto - clean dog
They are only ever washed if they smell really rank and only with human baby shampoo. If a shampoo is not fit for humans because of its chemical content, it's not fit for my dogs.