What does prevently mean in this paragraph? The original article can be found here:
[...] Only the activity of insects and frogs that danced around the lilly pads disturbed the water. Hardly a minute had passed when a movement caught the corner of my left eye. Imagination told me that a grandaddy beaver was tromping in clear range of my Winchester Super-X CXP3 power-point game load. Reality told me something else. What I had supposed was a large beaver turned out to be the head of a much larger animal. It was the presence of this laviathon that had prevently me from seeing any beavers upon arrival. In a flash, the five-foot reptilian sprang from the brush and exploded into the water with great speed and noise.[...]

