Good Luck Bob

Waterfowl hunting in Idaho can be excellent and, because this state has no national reputation for waterfowl hunting, competition for birds and good spots is usually light.
Idaho lies between the Pacific Flyway and the Central Flyway. Moreover, the southern part of the state is semi-arid. This is not a place you would expect to find under a big X on an old duck hunter's map. State waterfowl stamp sales have been running at just over 17,000 in recent years, making waterfowlers a tiny minority among Idaho hunters. So what we don't have is a bunch of waterfowl hunters; what we do have is pretty fair waterfowling and limits as generous as any allowed by the U.S Fish and Wildlife Service.
Where and when to go:

The first thing to know is that you have to figure it out for yourself. No outfitting or guiding for waterfowl is allowed in Idaho.

The second thing to keep in mind is the general weather pattern. Northern Idaho and eastern Idaho, especially the southeast, offer good numbers of birds but the water in these areas tends to freeze early. Most years will find you shut out around Thanksgiving. Get it while it's hot.

Birds tend to be a little lackadaisical about getting to the southcentral and southwest parts of the state, though early season hunting can be reasonably good for local ducks and geese. When the rest of the state freezes up, bird numbers along the big rivers and on the reservoirs in these two sections begin to rise. Northern birds join the locals sometime around Thanksgiving and shooting picks up. Some local waterfowlers don't even break out the waders until the turkey is et. Unless the weather becomes really tough and snow covers the feeding fields, ducks and geese alike will consider this part of Idaho the sunny south and stay the winter.
Finding the best waterfowling areas in Idaho is as easy as opening a map. Look for federal refuges. The refuges were established where they are because waterfowl were using the areas. Birds stay, in part, because the refuges give them the resting areas they need. Most of the refuges themselves offer good waterfowl hunting; nearby fields and smaller waters are worth scouting. Arguably the best waterfowl hunting in Idaho is not on a federal refuge but on the Fort Hall Reservation near American Falls. Here you will need a license issued by the tribe at considerable cost (presently around $475 which includes a $100 deposit that you will get back if no laws are broken - and cost is subject to change with minimal notice). Check out Idaho Fish and Game's Wildlife Management Areas as well. Along the Snake River, these public use areas tend to hold good waterfowling.

What Idaho has to offer the waterfowler:
Canada geese and mallards are the most sought-after species and, happily, the most common in Idaho. Both species produce huntable numbers within the state and are augmented by migrants from southern Alberta and Montana. If the wind is just right, British Columbia sends birds as well.
Pintails were also important before their continent-wide decline and may be so again as duck numbers rise generally. Few snowgeese are shot in Idaho, tending to stop rarely during the season but collecting in large numbers in eastern Idaho on their way back to the Arctic in early spring. Gadwall and widgeon are common and can be locally plentiful, especially along the Snake River. Widgeon seem to be on a sudden increase. Greenwing teal can be counted on to cost you too many shells, even late into the season but cinammon and bluewings tend to use Idaho as a nursery before heading south prior to opening day. Diver enthusiasts will want to be somewhere else in the country but canvasback, redheads and bluebills, especially bluebills, are locally available on the big lakes of northern Idaho and along the Snake River. Buffleheads and their cousins can be found in fair numbers almost anywhere all winter but Idaho tradition is to scoff at those who shoot at them.