Interdaily water temperature variations were studied at a known spawning site of European grayling (Thymallus thymallus) in the Große Mühl River, Austria. Spawning activity was visually observed from a bridge where spawners were counted and their activity/behaviour documented twice a day. The spawning of grayling was documented for a temperature range of 7.8–11.5°C. Analysis of the collected data showed that spawning activity increases significantly when water temperatures rise during a day. In addition, the results showed a significant response in the relative water temperature increase, which was +3.5°C on average; however, the absolute temperature between periods of non‐activity and spawning activity exhibited no significant differences.