While doing some research about the River Thames for the Storymap project, I learned that it is named as one of the cleanest rivers in all of Europe. However, about 70 years ago, it was considered to be a lost cause due to the World War II bombings. Methane gas was able to seep into the river and the toxins were even able to destroy the propellers off boats. England was able to get its act together to clean up the river through the next couple of decades.