Minecraft wiki entry for Salmon, associated text: Salmon spawn underwater at 12–32 blocks away from the player. Salmon spawn in groups of 3–5 in lukewarm, cold, normal, frozen oceans, their deep variants and rivers (including frozen rivers). In addition, salmon spawn on the surface (i.e., there must not be a spawnable block above the spawn location with a non-solid block on top). Salmon spawn in small, normal, and large sizes. 31.5% spawn as small, 52.6% spawn as normal, and 15.7% spawn as large.