He diverted a river. Too damn lazy to muck it out with a spade. Clearly not as lazy as the king, though.

The fifth labour that Eurystheus prescribed was to carry out the dung of the cattle of King Augeas of Elis in a single day, without the assistance of any other man. Some have thought that this labour was conceived to specially humiliate Heracles by making him carry upon his shoulders the cattle's dung, and that this is the reason why Heracles, declining the task as unworthy to be done by his own hands, turned the course of the rivers Alpheus and Peneus into the stables, cleansing them by the rivers' streams. It is told that Heracles did not reveal to King Augeas that he was under Eurystheus' command, and that he offered him to clean in one day the enormous mass of dung which had accumulated in the stables, if Augeas would give him the tenth part of the cattle. Augeas, who did not believe that possible, agreed; but when he learned that the task had been accomplished at Eurystheus' command, he not only refused to pay but also denied that he had promised it. For this reason arbitrators were called; and during the trial, Augeas' son Phyleus witnessed against his father. That was too much for King Augeas, who without awaiting the verdict, expelled both his son and Heracles from Elis. Taking what had happened into account, Eurystheus refused to admit the validity of this labour, alleging that Heracles had been hired by Augeas.

Apparently King Augeas had no idea recycling.

He needed the money.