A hook-setting device, including a flange that is fixed and generally transverse to a fishing line or leader, is adapted to resist the force of a fish strike on a hook or fly and to also indicate a strike by its movement in the water. The flange preferably floats at or near the top of the water, in a partially-submerged position, with a generally concave front surface facing the hook or fly. The front surface forms an open cup-shape that partially or completely fills with water, thereby providing resistance to the flange being pulled through the water and thereby setting the hook/fly in the fish's mouth. The preferred flange also features a generally convex rear surface facing away from the hook or fly, which rear surface is the leading surface during fly-casting, reducing air resistance during the cast and contributing to proper laying-out of the fly at the end of the cast. The preferred flange is fixed to the line or leader so that it does not move relative to the line/leader during casting, lay-out, fish strike, or at any time during use. A float may be attached to the flange, to increase buoyancy of the device; preferably, the float is coaxial with the flange and fixed to the rear surface of the flange so that there is no movement of the float relative to the flange or to the line/leader. Preferably, there is no structure between the flange front surface and the fly or hook, especially no structure that resides in, or slides into or out of the generally concave interior space of the flange, that would interfere with the interior space immediately filling with water upon lay-out and immediately providing resistance to a fish strike.