Hello there!
So, where the people settled, the place was very swamp. The water was very bad to drink. A lot of people got seawater poisoning, because they were drinking seawater. They also caught a lot of infections, and got poisoned. There were bad problems with mosquitoes and other bugs. In the area, there was not a lot of animals, so when they came, soon after there were no animals to hunt for.
Hope this information is enough.
-Sammy