These are some mammals you are likely to see in and around the water.
More: Mammals ...
Muskrat
Muskrats are common across the state. While considerably bigger than plain old rats, they are nowhere near the size of beavers, which can get to 50 pounds. Muskrats have tails that are slightly flattened from side to side, unlike beavers which have broad flat tails. Both animals build conical houses in the water, but only beavers build dams.
-- Wikipedia
More: Muskrat & Beaver ...
River Otter
Otters are aquatic weasels. You may find them climbing around on banks, or splashing around in the water, especially around dusk.
More: Otter & Raccoon ...
Harbor Seal
Harbor seals are not uncommon in the winter, but kayaking is, so don't expect to encounter them when you are out for a paddle.
More: Seals & Dolphins ...
This is for sit-on-top kayaks with closed hulls. Open-hull sit-inside kayaks don't really need hatches.
You can order any kind and size of hatch on eBay. They are easy to install - just trace the hole on the hull and cut it out with a jigsaw. A hatch like this one has a storage bag for small items like keys and phone, which removes for access to the inside of the hull.
More: Hatches & Storage ...