Water bodies were commonly considered deities during antiquity, this is Oceano (first or second century Ad).
Heracles obviously was capable not only of slaughtering monsters but also of capturing them, Erystheus thus had to try to find the hero’s weakness in yet another way. The fifth labour can therefore be considered as an attempt to take away some of Heracles honour since it seemed as there was no way to get through it with clean hands.
The challenge this time was to clean the stables of Augeas in one day, which seemed impossible as Augeas cattle was so numerous that they covered most of his land with dung, making it impossible to cultivate (Paus. V.1.9).
Heracles faced the task by meeting with Augeas, offering him to clean the stables in one day. They also agreed on a reward, a tenth of the cattle (Apollod. Epit. II.5.5) or a piece of land (Paus. V.1.9) - this would be of importance later. Now the hero couldn’t clean out all the dung himself in one day so he took help of two nearby rivers, Alpheus and Peneus (Apollod. Epit. II.5.5) or the river Menius (Paus. V.1.10) (remember that rivers were considered a type of deities).
Augeas However refused to reward the hero, why is unclear and several reasons given such as that Heracles cleaned the stables on the order of Eurystheus (Apollod. II.5.5), the he accomplished it by cunning (Paus. V.1.9), or that he had divine helpers. Heracles was expelled (with Augeas sons, as they defended Heracles right to the reward). The hero wasn’t content though, he marched on Augeas and killed him. Then he founded the Olympian Games during the victory celebrations.