1.4.  Etymology of water police, navigation police, port police and nautical police:

"Water police", also known as "nautical police", "navigation police" are synonyms that originated before the 19^th century.

 "Water police" came from  water + police. The term freshwater got into standard English usage around the early 19th century. Earliest publications we could find were published around the 1800s. Some of which include:

• Votes & Proceedings - Volume 2 By New South Wales. Parliament. Legislative Council · published in 1800. "Water police" was used in page 248, in the excerpt:  “... Water Police Office Clerk and Accountant…"

"Navigation Police" came from  navigation + police. "Nautical Police" came from  Nautical + police. Both terms got into standard English usage around the early 19th century. Earliest publications we could find were published around the 1800s. Some of which include:

• A Treatise on the Police of the Metropolis; ... The Sixth Edition, Corrected and Considerably Enlarged. By P. Colquhoun, ... By Patrick Colquhoun · published in 1800. " Navigation Police " was used in page 248, in the excerpt:  “... Navigation Police of the River Thames…" .  
• A Treatise on the Commerce and Police of the River Thames: Containing an Historical View of the Trade of the Port of London ... With an Account of the Functions of the Various Magistrates and Corporations Exercising Jurisdiction on the River ... By Patrick Colquhoun . published in 1800.  " Nautical Police " was used in page vi, in the excerpt:  “... If these objects shall be attained by a correct System of Nautical Police and by a sense of the …"