The piling of 56 foundations for 55 windmills and one offshore platform at the Blighbank (Belgian part of the North Sea, BPNS) has been surveyed for underwater noise. Maximum peak Sound Pressure Levels (SPL) up to 196 dB re 1μPa were recorded at 520 m from the piling location. The extrapolated apparent source SPL was estimated at 270.7 dB re 1μPa (95% CI: 260.4 – 281.1 dB re 1μPa), although such an extrapolation of the measured levels to the near field (< 100 m) environment should be interpreted with care. It is confirmed that the underwater noise level is a reason for concern, at least for marine mammals such as porpoises, seasonally abundant around the construction area. It is however very difficult to quantify and qualify the effects of the increased underwater noise level on components of the ecosystem, and a continued effort to do so is needed. To fine tune our estimates of noise propagation in the bathymetrically complex BPNS, in future more attention will be paid to the attenuation characteristics of underwater noise.