Sometimes they do, actually. For some lotad, it’s much like using a weighted blanket or getting petted: it’s a source of constant physical contact. Just make sure she doesn’t carry anything too heavy, and it wouldn’t hurt to give her a little extra actual physical contact (with petting and so forth) now and then.
Best of luck!
Well, I can tell you right off the bat that mareanie and binacle are marine pokémon. They won’t exactly die if you try to keep them in fresh water (that is, rivers or presumably the canals you’re thinking of), but they won’t exactly thrive either. So because you have a choice in the matter, I would suggest avoiding those.
Of the remaining two, shellos (while also technically a marine pokémon) does excellently in rivers and canals—the colder and cleaner, the better. This pokémon is native to colder regions such as Sinnoh, so it adores fresh, flowing waters, especially those fed by snowmelt. Meanwhile, lotad is a far gentler pokémon that is often more content with drifting … which means it runs a risk of being caught up in a river’s ebb and flow.
Additionally, lotad, being part-grass, don’t fare as well in polluted waters, so if you’re planning on letting your lotad out in the waters near your home, you may wish to keep it away from the canals unless your city’s canals are particularly well-maintained (and perhaps not even then). Shellos, on the other hand, are far hardier and can withstand polluted water (although, yes, it prefers unpolluted, as noted above).
That isn’t to say lotad isn’t a worthy partner. Many trainers prefer lotad for their easygoing dispositions, which make them rather easy to care for on land. In fact, so long as you have calm water and food, a lotad will typically be perfectly content. Some people even feel that just looking at a lotad floating happily in the water is calm and soothing to them, so lotad tend to be popular choices for homes near slow-running rivers or at least backyard ponds.
By contrast, shellos do actually require some level of basic care beyond food and water, including daily affection, grooming (simply wipe a wet towel across their bodies to remove excess mucus or debris), and exercise, and it’s not unusual for curious shellos to escape any enclosure you put them in (which means you may need to keep your poké ball on hand to prevent a curious shellos from wandering too far from home).
Finally, there are the evolutions to consider. Gastrodon is a beautiful pokémon often admired by collectors due to its bright colors, and for non-collectors, it’s even hardier than its preevolution and can thrive in practically any sort of body of water. On the other hand, it doesn’t fare too well out of the water, and it requires constant hydration. Meanwhile, lotad becomes progressively more amphibious as it climbs its evolutionary ladder, but if you were hoping for something peaceful and lethargic, you’ll need to stop at lombre and avoid giving your pokémon a water stone if at all possible. Ludicolo is a high-energy pokémon that can be quite a handful for trainers who aren’t also energetic.
In short, get a shellos if you want a hardy, energetic pokémon and don’t mind keeping it in water at all times after it evolves. Get a lotad if you want peace, a pokémon that’s easy to care for, or a dance partner later on down the line.
Best of luck!
Lotad
The Water Weed Pokémon
Type: Water/Grass
Official Registration #: 270
Entry: This small, lily pad-like pokémon thrives in the fresh waters of slow-moving streams and ponds. Friendly in nature, lotad like to use the broad lily pad adorning their heads to ferry pokémon across their watery habitat from one shore to another. Unfortunately, given that lotad weigh only five and a half pounds and therefore don’t actually have the strength to support many other pokémon, this is often more difficult than they would think.
Lombre
The Jolly Pokémon
Type: Water/Grass
Official Registration #: 271
Entry: The evolved form of lotad, by battle experience. This nocturnal pokémon spends most of the day underwater, sleeping upon a bed of aquatic moss as its pad soaks up sunlight. In this position, its diminutive stature is sometimes distorted by the surface of the water, causing many anglers to mistake lombre for drowned children, particularly by the Hoennian anglers who find them. Of course, given the fact that lombre’s skin is clearly grass-green (and not in the same way that skin appears after a human body is left to decompose underwater), the fact that a lily pad is permanently affixed to its head, and the fact that lombre is not actually otherwise child-shaped, the author fails to see exactly how lombre may be mistaken for a human child, but he’s not one to question the observations of Hoennian anglers. When they’re within earshot, anyway.
Ludicolo
The Carefree Pokémon
Type: Water/Grass
Official Registration #: 272
Entry: The evolved form of lombre, by exposure to water stone. True to its species designation, ludicolo is a notoriously carefree pokémon that is prone to dancing upon hearing a good beat. Even in the heat of battle, if it hears music, it will burst into a wild, rhythmic dance, and it will not be able to stop until long after the music has ended. One would think this is a disadvantage to the ludicolo, but in truth, it’s actually more of a disadvantage to their opponents. Apparently, ludicolo can beat an opponent into the ground normally, but their power increases if they, quite literally, stomp their enemies into the ground instead. Through salsa dancing.
As with all grass- or water-types, members of the lotad line need clean water—a lot of it, in fact. An outdoor pond would be ideal, but if this isn’t an option for you, be sure to get a shallow tank that’s wide enough for your lotad to move. Many trainers make the mistake of either getting a tank that’s too small or assuming that a lotad tank is the same as a fish tank, so be sure that you’re buying a tank that’s specifically marketed to surface-dwelling water-types. Either way, lotad will need a lot of space, so they’re not actually ideal urban pokémon unless you have convenient access to a park with a clean pond.
Also note that your lotad will need to spend plenty of time in water and sunlight. Ideally, this means six to eight hours of floating during the day, but it’s possible to separate its sunning times from its soaking times (such as in the case of indoor lotad). If you do this, you will still need to give it at least six hours of each, but if you need to leave your lotad unattended, simply allow it to float in its tank while you’re gone. While lotad generally need plenty of space, many of them won’t move too far from their tanks by themselves, so you can be sure that your lotad will still be there when you get back.
Standard lotad kibble is fine to give your new pokémon, but should you wish to feed yours something other than dry food, lotad are omnivorous and primarily eat berries and insects. Freeze-dried insects are fine, especially because lotad can’t generally tell the difference. Do not feed them anything large or hard (such as larger fruits or pieces of meat) as lotad don’t actually have teeth and rely on what their beaks can mash up to eat.
Upon evolution, lombre is a little less active than lotad and will thus be easier to handle; once you leave your lombre someplace, it will generally stay put without moving. Doubly so if you leave it in direct sunlight. However, ludicolo are extremely difficult to maintain in smaller, urban environments, as evolution increases their energy and stamina and causes them to experience uncontrollable urges to dance, especially around festive music. If you live in an urban environment, it’s highly recommended that you avoid allowing your lombre to come in contact with water stone. Should this happen anyway, clear an area specifically for your ludicolo. A completely empty bedroom should be sufficient. Soundproof this room (for the sake of your neighbors) and usher your ludicolo into it as soon as it looks like it’s about to dance.
Good luck with your new lotad, @slime-beast.
The Pokédex According to Bill 