you are likely to find Pollution in/at/on Lake. Lake is a type of Site. Tree is a type of Site. you are likely to find Snake in/at/on Tree. 
Run is etymologically related to Random. Run is a type of Trip. 
Pollution --AtLocation--> Lake --IsA--> Site <--IsA-- Tree <--AtLocation-- Snake 
Random <--EtymologicallyRelatedTo-- Run --IsA--> Trip 