I can't say I'm against people fishing from the pontoons at boat ramps but they need to realise they are there for boats and they need to get out of the way for boats coming in/out.
I'm not so sure swimming is a good idea especially when there are boats and propellers in the water. Boats have plenty of blind spots and you would never see a kid who just swum underneath the pontoon when you are coming along side.
Two recent instances that have happened to me that makes me against it which is typical of a few ruining it for everyone.
1. I was coming back in from a mornings fishing and there were two guys taking up half of the only pontoon with chilly bins, chairs and tackle boxes plus bait all over the pontoon itself. Neither of them pulled in their lines for me to come alongside the most accessible side of the pontoon. I pulled the boat forward as far as I could and tied it off out of their way while I went and got the trailer. Which is were the second issue became apparent. They had backed their car right up to the start of the pontoon partially blocking both of the narrow lanes. I only just managed to squeeze through but the guys fishing off the pontoon had zero interest in moving the car.
2. Again coming back in after a mornings fishing and there were a couple of kids swimming in the ramp who totally ignored boats trying to come in that side of the pontoon as well as trailers being backed into where they were swimming making any boat who tried to use that lane have to take the boat back out and around the other side of the pontoon. The thing that really got me was that the kids parents were watching from a distance while the kids swam in Gumboots of all things. This ramp has a lot of current which can make it difficult to come along side at times and the ignorance of the parents quite possibly could have killed their children if they had happened to get caught in the current. Surely the kids could have just swum at the beach were the playground is 100m away?