User blog comment:Lord Loss/Discussion of the Week: Swamps/@comment-184.38.31.4-20120714225442/@comment-5043481-20120715173509

The top of marshes are actually quite hard and load bearing because of all the sea plants growing on them, so large monsters would not be a problem. In the rills (muddy rivers formed when the tide drains through them) though the mud can get soft, sometimes soft enough to sink into slightly. Also it is really slippery, so large monsters would probobly fall over.