Irrawaddy Dolphin Watching
There are only around 85 dolphins in the Mekong, but there is a very good chance to see some at Kampi. As river dolphins, these animals don't generally approach boats show curiosity towards tourist boats like some marine dolphins do. There is no best time of day to see the dolphins as their activity patterns don't change much over the course of the day, though it can be pleasant with the setting sun late in the day, and fiercely hot in the early afternoon. The dry season offers generally better opportunities to see groups together and spectacular behaviour rare though it is, and in wet season the boat trip is considerably longer as the animals move several kilometers upstream from the tourist site. To protect the dolphins, you should ensure that your boatmen follows the dolphin watching guidelines provided and only use oars when near the dolphins. There's also a nice little shop which does benefit the community and helps encourage the villagers conserve the remaining dolphins. By motodop, this trip should be around US$2-4 for the round trip, about 20 min each way. Or rent a motorbike for US$5. Cycling to this spot should take about 60 min, bicycles are available for rent in Kratie and cost about 5,000 riel a day. When planning to do the Mekong Discovery Trail, keep in mind that you can also see dolphins from Koh Rougniv island, which nicely combines with a homestay in Koh Phdau. You get a private, and romantic, sunset tour with no other tourists in sight for US$7 per boat.
Bird Watching
If you are interested in birds, when on the boat, go upstream to the islands to look for the Mekong Wagtail Motacilla samveasnae, a Cambodian endemic species that can be found in this stretch of the river. Early morning might find them hopping on rocks near the dolphin area.
Basketball and Volleyball
There's a basketball and volleyball area on the south side of the old Governor's residence. The security guards probably won't refuse a civil request to use it within reasonable hours, and they might even join in.