So what is the boards' experience with the topo map designations of marsh/swamps and real life?

My google earth time and searching seems to look like a lot of the land designated marsh is just a grassy area.

Any comments? Are the fed topo maps right or educated guesses that often or not are wrong a little?

Well, in my own observations swamps and marshes marked on maps can be "grey" area to some extent. IMHO I think they are drawn on maps that way purposefully. When you think about it swamp and marsh are simply lowlands that collect and hold water. Depending on the water levels at the time you're there they could easily be larger or smaller than what is portrayed on your map. In any case I think cartography in general would highlight that feature to an "educated estimate" size based on surrounding terrain. So yes, it's unlikely to be completely accurate.

Wildlife, trees, water flow and many other natural occurrences can also change the size and shape of a marsh annually. A beaver can change a small stream into a large marsh of backwater in a matter of weeks. On a map it might look like a small low area until you get there and find it more like a small lake. A trapper decimating the beaver can change it back almost as quickly.

Don't be fooled into thinking they're just "grassy areas" on your map. From the air a bog can easily look like a grassy field, but can be difficult, even impossible, and downright dangerous to cross on foot. Bogs can float on many feet of dark murky swamp water that's just barely covered by the grassy surface.

Also look at the revision dates on the maps. Marshy areas change over time and often fill in and become less marshy. Some of the topos of wilderness areas aren't updated often due to a lack of funding. When they are updated it is generally from air photos and so it can depend on what it looks like when the photos are flown.

I take all I see on maps and Google Earth as approximations of what will be there. A swamp can stiffen into a field with drought and a field can moisten into a swamp with rain. JJ47 makes a great point about a beaver dam. I paddled a lake one year and launched right beside the forest service road. The next year, a broken dam meant the lower bay was gone and I had to bushwhack to reach water.

We came thru Deux Rivieries which is supposed to be a river in Quetico however due to beaver activity and dams it had turned into a swamp in the lower 1/3 of it with barely enough water to paddle thru it. Plus the reed/grass growth in that area made it difficult to know where the main channel was. At one point I had to get out and walk in about 6 inches of water and a foot or two of mud to get us where we needed to go. So just because it shows or doesn't show something on a map you have to take it with a grain of salt.

Most of the maps were drawn decades ago. For the most things don't change much up there. But they do update maps especially in concern with marsh ares. Anything new is highlighted in purple color. I find a lot of map updates with that color added. This is so hard to track on a map because it is fluid, sorry. A landmark, lake or hill hardly will change on a map, but depending on how much rain the area has got could mean a marsh or a field.

Are you generally thinking of BWCA or Quetico or both?

When I see a marsh on any sort of topo map I look at that area as a big wild card but I usually assume travel will be difficult at best.

It hasn't come up a lot during my BWCA travels more so while hunting in various parts of northern MN. I'll pre-scout areas from home using topo maps and also google satellite imagery and I'll try to determine some likely hunting spots and also avenues of travel. If it has been very dry then some marshes do turn into essentially a grass field and foot travel is fairly easy. If its a wet year they can almost turn into small lakes that you could maybe even paddle if you had to. Most of the time they are somewhere in between making foot travel and canoe travel next to impossible.

Even with all that said I've run into several instances where all indications during my pre-scouting on maps and imagery and taking into account recent weather told me a marsh should be fairly dry. When I actually walk up to it I see that all of the information I had and assumptions I made were wrong and that the marsh is still very wet. You just never know for sure until you get boots on the ground and check it out in person.

A really magical place we canoed through in the BW, a drowned forest due to a beaver dam being built, became a hellish mud hole a year later when the dam broke. I'm sure it was just a pleasant forest before the beaver got active and then vanished.

In another place, we've watched a small pond have its dam fail and turn into a marsh, a meadow, and now a young forest over a decade.

So, yes beavers are a big, changeable impact.