PS: The mushy thing they're standing on might be a cluster of Giant Salvinia, a floating water plant that can create extemely buoyant "islands" up to 60 cm thick.
Given its been identified as likely being a floating mat, which are apparently environmentally protected and present a risk of drowning.. I'd say there's a lot of stupid choices happening in this video.
I don't go to natural bodies of water much. Why does it have a drowning risk?
As someone in a warm climate, I'd be terrified of brain eating amoebas. Based on the foliage in the background though I'd bet they live in a cooler climate with much less risk of that.
I may mistake it with something but basically, it can trap you underwater. It's muddy so you can get stuck and...well. Recall the part where they stand on slowly sinking part.