Will a small in ground bog that houses frogs and tadpoles smell without filtration?

Question:I want to make a 4'x 3' rectangular bog that would house and breed green frogs. I live in Toronto. I want a deep level about 3' and a shallow bog like part. It would be helpful if you gave me directions on making a bog. To keep the bog moist i would just water it.

Answers:
I have a 3' x 5' stillwater pond that is about 2' deep. It hosts minnows (great for eating mosquito larvae...I garantee that no mosquitos emerge from that pond...I've even seen the minnows take an adult that alights on the surface to lay eggs), a few crayish, and tadpoles, as well as an assortment of water plants.

You'll want a few oxygenator plants (they grow submerged in the water), and some "floaters", like water lettuce, water hyacinth, or water lillies. (The lilly-pad plants need to be contained, and removed at least once a year, culled down to a small plant before restocking - otherwise they will eat your pond within 3 years.)

The oxygenators do what their name suggests, and the floaters provide shade. A still water pond in full sun will quickly fill up with algae. The tadpoles sometimes grow into frogs, and they'll lay eggs, but the frogs often find the size of the pond way too confining, and they'll move on after a month or two.

Keep a good biological balance, and you'll have a beautiful water garden. I have only known mine to smell briefly in the spring right after it warms up - if there are plants that died over the winter and are now un-thawed and rotting in the water.

Otherwise, I've never known it to have a smell. It also attracts dragonflies, lots and lots of birds, and other wildlife.