There are two Port Orleans resorts next to each other on the Sassagoula River. At the end of the line is Port Orleans Riverside. Just down the river a tiny bit is Port Orleans French Quarter. And then down the river about a 10 minute ride away is Downtown Disney.
At roughly 9:00 a.m., boat service starts between the two Port Orleans resorts. At roughly 11:00 a.m., boat service starts between these resorts and Downtown Disney, and stops around 11:00 p.m. or a tad earlier.
Boats coming from DTD will stop at DTD first and will then go on to POR. Boats going to DTD start at POR and stop at POFQ along the way before getting to DTD. So it's not uncommon to be in line at the dock at POFQ but only a few people are able to get onto the DTD-bound boat because it is mostly full with POR folks.
The boats don't run in inclement weather, but there is always bus service.