Frogs have skin that's SEMI-PERMEABLE, this means that some things are absorbed into their body. Chemicals and pollution in rivers affect frogs and their tadpoles because of this. We looked at what species of frogs we should find in our stream, and were shocked when we didn't find any! What other species have been affected by the pollution and litter in our township? We will have to find out... good thing the frogs have alerted us to this potential problem!