Day trips on the Tonle Sap Lake fall into two categories, so be careful what you're signing up for. First, avoid the 1 1/2-hour tours out of the boat ferry jetty, Chon Khneas. These trips sound like fun, and for just $15 per boat or $10 per person, you can go with a driver and guide out onto the Tonle Sap. You do glimpse a bit of river life, the net-twirling fishermen, floating schools donated by Korean NGOs, and the commercial boat traffic on the Tonle Sap's main inlet, but once out on the water of the lake you get a quick ride among ethnic Vietnamese, Khmer houseboats, and fisherman, then stop at a large tourist-trap barge with crocodile pits, small fish farms, perhaps an aquarium with some sickly looking turtles, snakes, and fish choking on dirty water. It's all about the $1 Coke or souvenirs you might buy. Not worth the trip, so be sure to avoid rides to just Chong Khneas. The only exception to this is the fine upmarket evening cruises along this same route through the company Terre Cambodge . The cost is $20 per person and doesn't include the good cocktails you might enjoy while watching the sun dip into the cool lake.
The best day trips are one of the many full-day options that take you to far-flung floating villages like Kampong Phluk in canoes among low mangrove or to a lush bird sanctuary, called Preak Toal. Following these routes with the larger tour operators comes with a hefty price tag for Cambodia, from $80 or so per day, but it's worth it.
Contact Terre Cambodge (www.terrecambodge.com) or talk with any of the budget tour operators in town (or your hotel's tour desk). All services are consolidated through the same providers so you get the same trip wherever you buy it. Be sure and specify the exact sights you want to see and any inclusions you'd like, such as lunch. One unique find is the folks at OSMOSE (www.osmosetonlesap.org), whose main focus is conservation but who run fine tours as well.
These trips are best in rainy season because the mangrove swamps are dried up at other times. The birds at the bird sanctuary are best viewed from December to April. The Tonle Sap basin is lush and green when the water recedes in the dry season, but the water is so low that getting around on the lake, which drops from 12m (39 ft.) down to 4m (13 ft.) in depth, and falls to a third of its rainy-season size, is quite difficult.
If you're connecting onward with Siem Reap or Battambang by boat, you'll get a glimpse of life along the aquatic byways of Cambodia. The road heading south to the lake follows the Siem Reap River and gives you a glimpse into communities of precarious stilt houses that look ready to totter any second, and farmers herding groups of domesticated ducks along canals. Getting to the boat, you'll follow a long dirt causeway lined with shanty houses and elbow among trucks overloaded with minnows and small fish caught in the lake, squishing and leaking and bouncing precariously. Once out on the open water on the speedboat to or from Phnom Penh, it's just hot sun and blue water -- not an especially picturesque ride, but fun when the water is high in the rainy season.