If you witness and want to report speeding on the Ottawa River/Bay waterway you contact the Ottawa Police Service (as you would a normal traffic complaint). They will refer to the Ottawa Police Marine/Dive/Trails Unit (MDTU). You can file on on-line Traffic Report (i.e. speeding on the water ways/Ottawa River).
The Ottawa Police Marine/Dive/Trails Unit (MDTU) is currently comprised of eight (8) full time members responsible for providing assistance to all divisions of the Ottawa Police in a timely manner.
The team searches for missing or drowned individuals, as well as provides forensic diving techniques to recover human remains, vehicles and discarded weapons. MDTU uses either S.C.U.B.A and Surface Supply Diving techniques in compliance with provincial and federal diving regulations as well as Ottawa Police Service policies and procedures.
The MDTU responds to complaints from the community as well as educates the public on water safety, regulations and speed enforcement (Historic Canals Act, the Small Vessel Regulation, Canada Shipping Act, Collision Regulations, the Liquor Act, and the Criminal Code among others).
Below is a screenshot from the online reporting tool, note the definition and the question asking if you are reporting an incident on a waterway.