*In “Instinct,” Elric sets up his refuge near a river.
*The facility in “Broken Ties” and “Reunion” was built near a river. Presumably, the one in “Spoils of War” was as well, because there is a canyon in the distance (also noted a CGI continuity error– the trees were not added in the end scene with the hive crashing into it). That cloning facility was likely older, left over from the time of the Ancients, and the river may have shifted away over the millennia.
*Todd, his tormented poetry mirroring Spike’s dedicated labor out in the desert in “Vegas,” notes, “No river. No water. Dry as a desert. Dirt is all around.”
*The cruiser in the end of “Michael” is parked near a lake.
It seems Wraith have an affinity for water, especially rivers when they know they are going to be setting up a permanent residence. Many Earth insects tend to like water. Salt water is harmful to Iratus bugs, but “Submersion” showed Taina’s cruiser’s hull withstood it for 10,000 years and she was a good swimmer. The decor of hiveship interiors is also reminiscent of aquascapes.
With flying vehicles equipped with storage beams, Wraith would not have need of using rivers as roads.
For all of the mist on board the hives and cruisers, presumably, water might be beneficial for the tech, for replenishment.
I also doubt taking lifeforce energy every 2-3 months would be sufficient to provide, if at all, enough moisture needed for essential biological functions, such as respiration.
Whatever the reason is, they certainly have an eye for natural beauty.