However, a video posted to YouTube by user Viva Frei shows many residents apparently did not follow the instructions.
The video shows more than a dozen used condoms floating in one small section of river.
"Who flushes condoms down the toilet to begin with?" the man filming asks, while panning the camera across the "endless" condoms.
"The city warned citizens not to flush bad stuff down the toilet (such as needles, condoms, tampons, etc.), as it would end up in the St. Lawrence River. Well, thanks to a nice West-East wind, all the filth pooled in the corner of the port in Old Montreal, and as you can see, there are condoms EVERYWHERE!" the user wrote in the video's description.