Not long ago, while fishing an Eastern CT trout stream, a fishing partner of mine, while standing midstream, was confronted by an adjacent landowner and told, "this is private property." This was despite a DEM posted sign stating that the public were entitled to access within 10' of the river bank. The landowner arrived streamside in an ATV of some type and wore a holster with a visible sidearm. The fisherman explained that he was within his legal right, below the high water mark, and not on private property. When the landowner asked to see his fishing license, my friend asked if he was a DEM or law enforcement official and did not produce his license. The verbal exchange ended and the landowner continued to sit streamside in his vehicle while my friend continued to fish for an hour or more. A phone call to DEM and to the resident state trooper the next day resulted in a visit to the landowner, with a caution not to harass anglers in this particular section of the river. The landowner on several other occassions continues to "visit" his property streamside when anglers are present, however without verbal exchange.
Wading fishermen should not be intimitated by such encounters and should know their legal rights: http://www.nationalrivers.org/us-law-public.htm This link is an excellent discussion on the subject.
While no one advocates confrontation, knowing your rights will lessen the intimidation factor that many of us have likely encountered as we search and wade our streams and rivers.