In the town of Khanom along the canal, there are mangroves, some of which are fairly easy to access just before the bridge. There you can walk on cemented paths raised in the middle of mangrove trees, colored crabs, jumping fish and also crab-eating monkeys even if they are more shy during the day (I did not see them but they really live there). Here, you can not go kayaking but you have a few kilometers further after the bridge, the restaurant Krua Tangke
that rent kayaks. It is also thsi restauant that offers the boat tours on the canal, including fireflies tour in the evening.
The place I give GPS coordonnates is quite small but as it is on the road to go to many must-see places and adjoins the city, it may be interesting to go.