In northern regions, water is used for winter road construction. Such withdrawals can reduce [oxygen] and water levels, impacting fishes. Regulatory withdrawal limits are largely theoretical. Thresholds were tested by removing 10% and 20% of the under-ice volumes from two small lakes and comparing oxygen parameters, temperature, over-wintering habitat, and northern pike (' Esox lucius') abundance to reference conditions. The 10% withdrawal resulted in a 0.2 m decline in the [oxygen] profile at 4 mg·1 -1, no effect on total oxygen mass, or over-wintering habitat. The 20% withdrawal caused 0.7 m reduction in the [oxygen] profile at 4 mg·1 -1, a 26% decline in oxygen mass, and a 23% decline of over-wintering habitat. Water temperatures were <= 10% colder in the upper strata in the year following the withdrawal in both withdrawal and reference lakes, so this effect is likely independent of treatments. Northern pike abundance was not impacted by the water withdrawals.