Cambodia’s 1900km of navigable waterways are not as important as they once were for the average tourist, given major road improvements. North of Phnom Penh, the Mekong is easily navigable as far as Kratie, but there are no longer regular passenger services on these routes, as buses have taken all the business. There are scenic boat services between Siem Reap and Battambang, and the Tonlé Sap lake is also navigable year-round, although only by smaller boats between March and July.
Traditionally the most popular boat services with foreigners are those that run between Phnom Penh and Siem Reap. The express services do the trip in as little as five hours. The first couple of hours out of Phnom Penh along the Tonlé Sap River are scenic, but it becomes less interesting when the river morphs into the Tonlé Sap lake, which is like a vast sea, offering little scenery. It’s more popular (and much cheaper) to take a bus on the paved road instead.
The small boat between Siem Reap and Battambang is more rewarding, as the river scenery is truly memorable, but it can take as long as a whole day with delays.