Research and development of a fish ladder for sturgeons requires understanding ladder hydraulics and sturgeon behaviour in the ladder to insure the ladder is safe and provides effective passage. After years of research and development, we designed and constructed a full‐scale prototype side‐baffle ladder inside a spiral flume (38.3 m long × 1 m wide × 1 m high) on a 6% (1 : 16.5) slope with a 1.92‐m rise in elevation (bottom to top) to test use by sturgeons. Twenty‐eight triangular side baffles, each extending part way across the flume, alternated from inside wall to outside wall down the ladder creating two major flow habitats: a continuous, sinusoidal flow down the ladder through the vertical openings of side‐baffles and an eddy below each side baffle. Ascent and behaviour was observed on 22 cultured Lake Sturgeon = LS (Acipenser fulvescens) repeatedly tested in groups as juveniles (as small as 105.1 cm TL, mean) or as adults (mean TL, 118 cm) during four periods (fall 2002 and 2003; spring 2003 and 2007). Percent of juveniles entering the ladder that ascended to the top was greater in spring (72.7%) than in fall (40.9–45.5%) and 90.9% of 11 adults, which ascended as juveniles, ascended to the top. Six LS (27.3%) never swam to the top and seven (31.8%) swam to the top in all tests, indicating great variability among individuals for ascent drive. Some LS swam directly to the top in <1 min, but most rested in an eddy during ascent. Juveniles swimming through outside wall baffle slots (mean velocity, 1.2 m s⁻¹) swam at 1.8–2.2 body lengths s⁻¹ and 3.2–3.3 tail beats s⁻¹, either at or approaching prolonged swimming speed. The side‐baffle ladder was stream‐like and provided key factors for a sturgeon ladder: a continuous flow and no full cross‐channel walls, abundant eddies for resting, an acceptable water depth, and a water velocity fish could ascend swimming 2 bl s⁻¹. A side‐baffle ladder passes LS and other moderate‐swimming fishes.