Can I use a net in the aid of recovering Waterfowl?

If I understand your question you are trying to retreive waterfowl with a net streched across a river stream.  Stretching a net across a waterway could present all types of problems for you and others.   Make sure you are contacting all private landowners prior to hunting to ensure you are not violating any trespass laws.  You also may want contact the county and local city authorities to make sure you are within all city and county ordinances.  Lastly you need to consider all the possible safety concerns to others using the waterway.  Stretching a net across a waterway could present a real hazard for others using that same waterway.  You would quite likely be libel for any incidents, damage or injuries caused to others or their equipment while using the same waterway.  In short I would recommend you consider a good bird dog for retrieval instead of the net.