Hello!
I found out that while the Spiderweb won't work underwater, it will slow you down/keep you from falling if you sprint from a Spiderweb outside into the water.
Within the water you will not sink and move very slowly, even while having cheese until you leave the water again..
Found this bug in map 131 - add a spiderweb to the right of the Icewall then sprint from the spiderweb into the water.

This might work with portals and water as well, but I was not able to test this yet as I did not know any maps with that combination of skills.

I've found webs to work very much like water, I side-climb up them the same way, to me i see them as a square of water "in slow motion" so it could be something to do with that maybe causing this?

*warning, squirrel is totally unqualified to answer this, knows nothing of the in depth working of the skills, and has never even opened the map editor so knows nothing of the background going-ons of terrain, this is just a speculation*