How to tell difference between a tortoise and a turtle?

I have a large pond with turtles, and I sometimes find one near the house, about 200 feet from the pond. So I take it back there and it swims off. Thing is I don't want to drown a tortoise, so how can I be sure of what I am picking up?
Answers:
most water turtles are green, except for the musk and snapping turtles, they have webbed feet with longer toenails and they usually have a flatter shell
the tortoises are usually brown or dark tan, they might have red, yellow or orange on their heads and their front legs, their legs look like elephants legs
all turtles and tortoises get in the water occasionally and it won't hurt a tortoise if you put it in the water, just make sure that it can get out of the pond and doesn't drown get a good book for references and photos

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1. There is absolutely NO reason to put ANY turtles back in the pond- they may be migrating looking for new territories and resources (does your pond have enough food for them all?) If they are in danger, put them closer to the pond, but always give them that option. That will automatically fix the problem!

2. Where do you live? Most places in the world only have a couple of native land-dwelling species of turtle. If you are in the US, the box turtles all have high-domed shells and hinges on their bellies. The Gopher, Desert, and other tortoises have elephant-like front legs, are generally rare, and are very protected. In some places, even picking one up is against the law.

Try the photo gallery at http://www.tortoise.org for pictures of various turtles and tortoises.