'swimming dog' and 'dog swimming'?

Solution 1:

If what you saw was a dog in water swimming, and were mentioning that, it would be correct to say a dog swimming; swimming being a present participle, indicating what the dog was doing. The dog was swimming

However if the ...ing form of verb is placed before the noun, swimming becomes an adjective qualifying the noun dog. Grammatically it could be one of two things:

a) The swimming dog could have been a certain type of dog which swims a lot. I saw a swimming dog does not necessarily mean the dog was swimming when you saw it. It was just a type of dog which swims (notwithstanding the fact that most dogs can swim)

b) It could mean the same thing as a dog swimming. But it would be an unusual way of expressing it. The normal idiomatic form would be a dog swimming.

Solution 2:

Consider this example-

1.I saw a lying man today.

2.I saw a man lying today.

In the first example lying is adjective.

In the second example lying is verb.

Hope this clears your doubt.