At the part of the tutorial where you can now battle and are exploring for materials the 2nd time. It says i should look for items in the water as well, such as shells . that's the issue, i try to go to the water but it doesn't let me. It'll let me move around the land but not on the water so i can't complete the task. Any help? 

Pets can't move in water, but they can pick items from water tiles right next to them. You need to move your pet near an item in water and click move button in the direction of that item.