I would think whoever owned or managed the ramp would keep it clean to avoid legal action. Maybe a light letter with undertones of legal action to the owner or government agency responsible for upkeep will do the job. Also contact the local newspaper or TV station. It's amazing how a little press prods people and government into action.
Down here they would probably just close the ramp.
Not only that, but why even bother with a legal thread.
Sorry but that is the worst recomendation. That is the reason the US is the way it is, so "class action legal suit feed the lawyers more money happy"
The second recomendation is the best one. Clean it up, that stuff comes off fairly easy. Use a rake, or a shovel. Back home we had that problem with boat ramps, we always had a shovel or a rake to scrape the stuff off. Takes around 10 mins. It is worth every minute, to avoid falls etc.
