I found this on the web. Hope it helps: ("I've deleted the bits that were not relevant.) "Tell-tale tails: If you see a nutria or muskrat out of the water, their tails may help you tell them apart, but it’s not as obvious as with beaver. If the critter has a big, thick, round, hairless rat’s tail – that’s nutria. The muskrat’s tail looks similar, but it is not as big, has more hair and is flattened vertically, not horizontally like a beaver’s. Sometimes the muskrat’s tail looks like a thick, dark ribbon, especially when it’s lying flat on the ground behind the animal. What the animal does with its tail when it is swimming is one of the best clues to identification. When a muskrat swims, it thrashes its tail back and forth and it looks like the muskrat’s head is being chased by a swimming garter snake. You can see that the muskrat’s tail is acting like a propeller, pushing it through the water. Muskrats swim with their tail because they do not have webbed feet, like the other two rodents. You usually don’t see nutria’s tail when it swims but if you do, part of it will just arch out of the water a bit and it won’t be moving much. Heads up What if all you can see is just a dark head moving through the water? It’s usually easy to tell if it is nutria’s head because nutria have several areas of light hair on their heads, while muskrat heads are solid, dark brown. One of the most obvious field marks on nutria is their big, white whiskers – and I mean big and bright white. I’ve never really been able to even see the black whiskers on swimming beaver and muskrat. Nutria often have lots of gray hair around their mouth, making them look like a hoary marmot or a man with a gray goatee. Sometimes the easiest field mark to see is a patch of lighter fur, usually tan to orange, that is at the base of the nutria’s ears. It looks a bit like their ears are glued on with some light tan caulking and makes the nutria’s ears stand out much more than on the other two." Other clues You would think that the general size differences between these animals would be a good clue, but it is very hard to accurately judge the size of these animals when they are swimming. Identification by size gets just about impossible in summer when there are baby beaver and nutria swimming around. If you think the critter you are seeing is an adult, and it is smaller than a house cat, it is a muskrat. If the critter is clearly bigger than a house cat, then it could be either nutria or beaver, which are hard to separate by size. It is easier to tell beaver and nutria apart by the other clues given here than to try to separate them by size. Both beaver and nutria can show their huge orange incisors. "
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Hi Dingodog,
That's exciting. I think it is a muskrat. I believe Nutria have been fully exterminated in Indiana around 1980. I have two links for you to explore.
1. Nutria Extermination and Persistence in the U.S.: http://www.nwrc.usgs.gov/special/nutria/....
2. Mammals of Indiana: https://www.extension.purdue.edu/extmedi...
Hope this helps!
(Sorry that's so long... but it was just crammed with really good info!)
I found this on the web. Hope it helps: ("I've deleted the bits that were not relevant.)
"Tell-tale tails:
If you see a nutria or muskrat out of the water, their tails may help you tell them apart, but it’s not as obvious as with beaver. If the critter has a big, thick, round, hairless rat’s tail – that’s nutria. The muskrat’s tail looks similar, but it is not as big, has more hair and is flattened vertically, not horizontally like a beaver’s. Sometimes the muskrat’s tail looks like a thick, dark ribbon, especially when it’s lying flat on the ground behind the animal.
What the animal does with its tail when it is swimming is one of the best clues to identification. When a muskrat swims, it thrashes its tail back and forth and it looks like the muskrat’s head is being chased by a swimming garter snake. You can see that the muskrat’s tail is acting like a propeller, pushing it through the water. Muskrats swim with their tail because they do not have webbed feet, like the other two rodents.
You usually don’t see nutria’s tail when it swims but if you do, part of it will just arch out of the water a bit and it won’t be moving much.
Heads up
What if all you can see is just a dark head moving through the water? It’s usually easy to tell if it is nutria’s head because nutria have several areas of light hair on their heads, while muskrat heads are solid, dark brown. One of the most obvious field marks on nutria is their big, white whiskers – and I mean big and bright white. I’ve never really been able to even see the black whiskers on swimming beaver and muskrat.
Nutria often have lots of gray hair around their mouth, making them look like a hoary marmot or a man with a gray goatee. Sometimes the easiest field mark to see is a patch of lighter fur, usually tan to orange, that is at the base of the nutria’s ears. It looks a bit like their ears are glued on with some light tan caulking and makes the nutria’s ears stand out much more than on the other two."
Other clues
You would think that the general size differences between these animals would be a good clue, but it is very hard to accurately judge the size of these animals when they are swimming. Identification by size gets just about impossible in summer when there are baby beaver and nutria swimming around. If you think the critter you are seeing is an adult, and it is smaller than a house cat, it is a muskrat. If the critter is clearly bigger than a house cat, then it could be either nutria or beaver, which are hard to separate by size. It is easier to tell beaver and nutria apart by the other clues given here than to try to separate them by size. Both beaver and nutria can show their huge orange incisors. "