Swamps of the Sicklands

Publisher's blurb:

New adventurers are traveling in hot grasslands among merchants. In a small town with a single store, there is a Help Wanted add. It offers 100 gold pieces, but the adventurers have to rid the area of a new type of goblin called Bull Frog Goblins. As the adventurers travel through diseased swamps, they find an old town falling to pieces. It is up to the adventurers to kill off the filthy goblins and finally rid the town of a disease known as "Swamp Gut". But beware! There are more than goblins that hide in those waters, and even the goblins are afraid to swim too deep.