Ok...The best I can do is give you the following which is the definition "Navigable" as outlined in the link.
"B. Navigable Inland Stream:
A navigable inland stream is (1) any stream declared navigable by the Michigan Supreme Court; (2) any stream included within the navigable waters of the United States by the U.S. Army Engineers for administration of the laws enacted by Congress for the protection and preservation of the navigable waters of the United States; (3) any stream which floated logs during the lumbering days, or a stream of sufficient capacity for the floating of logs in the condition which it generally appears by nature, notwithstanding there may be times when it becomes too dry or shallow for that purpose; (4) any stream having an average flow of approximately 41 cubic feet per second, an average width of some 30 feet, an average depth of about one foot, capacity of floatage during spring seasonal periods of high water limited to loose logs, ties and similar products, used for fishing by the public for an extended period of time, and stocked with fish by the state; (5) any stream which has been or is susceptible to navigation by boats for purposes of commerce or travel; (6) all streams meandered by the General Land Office Survey in the mid 1800's. Moore v Sanborne, 2 Mich. 520 (1853); Thunder Bay River Booming Co. v Speechly, 31 Mich. 335 (1875); Stofflet v Estes, 104 Mich. 208; 62 NW 347 (1895); Cole v Dooley, 137 Mich. 419;100 NW 561 (1904); Sterling v Jackson, 69 Mich. 488; 37 NW 845 (1888); Collins v Gerhardt, 237 Mich. 38; 211 NW 115 (1926); Rushton ex rel Hoffmaster v Taggart, 306 Mich. 432; 11 NW2d 193 (1943); Diana Shooting Club v Husting, 156 Wis. 261; 145 NW 816 (1914); Muench v Public Service Comm., 261 Wis. 492; 55 NW2d 514 (1952); Nekoosa-Edwards Paper Co. v Railroad Comm., 201 Wis. 40; 228 NW 631 (1930); Lamprey v Metcalf, 52 Minn. 181; 53 NW 1139 (1893); Kelley v Hallden, 51 Mich. App. 176; 214 NW2d 856 (1974)."
As it looks now, this is the only definition of what a navigable stream is. I guess you would have to apply this definition to the stream you are referring to and make your decision from that.
But if you said the landowner seems to be nice, it might not hurt to ask for permission from him to confirm that its OK to be there.
HM