Disclosed herein is a training fin for assisting a wide variety of swimmers to gain a superior cardiovascular workout with minimal risk of injury. The fin has a proximal end and a distal end. Additionally, the fin has a dorsal section and a plantar section and defines an opening for insertion of a user's foot adjacent the proximal end. The dorsal section has proximal and distal ends aligned with the proximal and distal ends of the fin. The dorsal section is solid from the proximal to distal ends. The dorsal section has side sections. The plantar section has proximal and distal ends aligned with the proximal and distal ends of the fin and dorsal section. The dorsal and plantar sections are joined, at least, at the proximal and side sections. The dorsal surface includes a fluid separator for increasing hydrodynamic design and function. In an exemplary embodiment, the fin defines a boot, made from pliable material. The pliable material being of varying thicknesses. The boot has a foot pocket and a blade portion. The foot pocket is sized and shaped for removable attachment to the foot. The blade portion is sized and shaped for swim training purposes and for transmitting propulsive forces created by a swimmer's leg to the foot and fin. The blade portion has a defined thickness. And, the foot pocket has a constant thickness and being thinner than the thickness of the blade portion.