There is one way across, that costs gold, and that can be a problem. If you get mugged on the other side, there is no way back.
As a monster NPC, I am currently, as I write this suggestion, up to my 15th+ minute of waiting for the goodly PCs on the other side of the crossing to walk away so I can cross (it automatically destealths you, so I will always be seen).
This is a bit dull.
I think Dill mentioned the possibility an alternate route might be made, involving canals and disease (or plague?) rolls. Perhaps a tiny underwater area with a chance of aquatic monsters, to make it fair and equal to 5 gold.
A crossing using a grapple gun and rope might also be appreciated, as well as ways to walk along the bottom of the canal to quests such as Snails, etc...
Choosing to swim across would be kind of a cool option and I could see some Peers maybe shunning the idea so as not to get their clothes dirty vs. Pond folk that just hold their nose and dive in. Could be interesting.
If swimming across had a mechanical malus such as a Disease Check and/or flies (it's swimming through muck after all) might be a good incentive to not take it over 5gp toll every single time.