Class I lever. The oar is fixed in the oarlock, the rower pulls on the handle, and the blade moves in the opposite direction to propel the boat. The blade is further from the oarlock than the rower's hands. So, the heavy force of a short rowing motion becomes a smaller force over a greater distance.

From an observer on the shore, the oar is instead a Class II lever. Here, the fulcrum is the blade, planted in the water. The rower pulls on the handle and the boat moves along with them. The "Class II" perspective is important