suggestions to agitate stream flow?

Hi, group.  I hope this is the correct newsgroup in which to post this.
We have some very slow-moving streams in a heavily wooded area (water
velocity maybe 1 mph) contaminated with VOCs (volatile organic compounds).
These VOCs can be stripped out of the water if agitation is introduced
such as by increase stream flow velocity, etc.  But the stream water flow,
being on a very slight grade, probably won't get too much faster by just
throwing obstacle like rocks in it.

Can anyone suggest an inexpensive way to agitate the water to strip out
these VOCs?  We have even considered low-powered air bubble systems but
would prefer to use some passive, natural way of increasing water
agitation.

TIA,

Bob