Those who don’t fish never suspect the potential at their doorstep: Tucked placidly into urban sprawls and cityscapes across the continent, a wealth of overlooked waterways beckon a certain breed of adventurer. Surrounded by a million souls, it’s that tiny pool of a park pond. Might be a diversion canal in Phoenix or Houston; a city lake encircled by picnic tables and ‘woggers’ in L.A.; a quirky little creek or an industrialized river coursing through Philadelphia, Kansas City or Milwaukee.…