Gehn uses the "Great Whark" as a symbol of his power. It induces superstituous fear to the Rivenese. Gehn has captured some as pets and feeds them with transgressors, usually at the Gallows on Jungle Island. At the later years however the population was greatly diminished.
Wahrk statues with offerings are found in the Temple of the Dome Island, and crude totems are found in the lake of the Plateau Island. In a cave of the Jungle Island there is a crude stone painting with a figure (Gehn) feeding people to the fishes. In the School Room there is a children's toy with two hanged men fed to a Wahrk. In the jungle there is a big wahrk idol which leads to a tram station or to the upper walkways and Gehn's watchtower.
It is no wonder that their population diminished, seeing the constructions from their bones and skulls all around Riven, such as the Wahrk Gallows and jawbones adorning Gehn's throne of his watchtower; and the huge amount of tusks (possibly from wahrks) adorning the shores of the artificial lake of the Survey Island.
The sound of a Wahrk hitting the Gallows can be heard. There is also a trapped wahrk in the underground lake of Survey Island; the kinetoscope in the lake doesn't line up with the spinning dome, due to an angry Wahrk ramming into it.
Wahrk bones can be seen in the New Mexico desert, suggesting one of them was sucked into the Star Fissure when Riven was destroyed.