Tonle Bati is a popular lake and picnic area that has bamboo shacks built out over the water that people can rent out for eating and whiling away the day. It's generally a weekend get-away spot, which means it's nice and quiet during the week. Locals swim there, but the water does not look real inviting. There are all kinds of food and drink stands that sell everything you need for a picnic along the lake.
Note that there are tours that follow you when you arrive on weekends and try to get you to go to their own place. It's best to pass right by them and find a spot on your own. Check prices beforehand on everything ? they are famous for handing you an outrageously high bill when you depart.Tonle Bati is a place of worship and features two ancient temples, Ta Promh and Yeay Peov, and a pagoda, Wat Tonle Bati, which was built in 1576.