Question

1. I called my brother, walking along the river.

2. I called my brother while I was walking along the river.

3. I called my brother while I walked along the river.
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Which one is closer to #1 in meaning, #2 or #3?

Answer 1

#1 means that your brother was walking along the river. Placement of the participle phrase needs to be as close as possible to the word it's modifying.

Therefore, only 2 and 3 work.

However, if you want 1 to have similar meaning to 2 and 3, you should phrase it like this:

Walking along the river, I called my brother.