Edge Effect

From Openwaterpedia

noun - the Edge Effect is the ability to swim (or move) faster at the edges of a pack (or group of individuals) relative to a position in the middle of the pack (or group). Swimming on the outer edges of a pack allows faster and easier movement. The Edge Effect allows individual at the sides of groups to move more quickly and navigate the pack (or crowds) more effectively at the edges. People start bumping into each other when crowd density reaches 7-10 square feet (0.65-0.92 square meters) per person and this hinders the flow in the middle.