I don't know every single canal in Amsterdam but Richard was last seen turning into the "Herengracht". Parked cars by the waterside, walking path on the other side of the road. The trees by the water might also attract a male to relieve himself, and so he can stumble in the water. Either way, if there was a danger for anyone you would also have female victims and not just drunk males IMO.I have walked many places right next to water with no railing.Amsterdam is famous for public urination and has public open urinals everywhere to deter going to the canals or urinating in the street.
Walking in not easy in Amsterdam you have 2 feet of sidewalk wide and another path for bikes.You really have to keep alert not to get run over by bikes,scooters or cars.Not alot of room for walking on sidewalks.

google translate
https://www.rtvnh.nl/nieuws/178933/...aar-vermiste-brit-hij-is-een-ervaren-reizigerWhen police he watched images from the cameras on the square. "Richard was alone. He crossed the street diagonally," says Lee. "He stumbled a little, but not so bad that he could not walk. He then disappeared from view. The last point is the corner of the Thorbeckeplein."