Clause

Guest,

After consulting Clauses: the Essential Building-Blocks, I believe the answer is no.

Quoting from the referenced web page.

Relative clauses are dependent clauses introduced by a Relative Pronoun (that, which, whichever, who, whoever, whom, whomever, whose, and of which).

"Crossing the stream" is a participial phrase. You can look for a definition of Participle and here at The Garden of Phrases for some examples of participial phrases.

I hope this helps.

MountainHiker