In many cases, dolphin tanks, like auditoriums, are designed with no special effort directed toward achieving acoustical perfection. Our measurements were to be made in a small pen in a large semicircular tank which was divided much the same as a railroad roundhouse, and contained seals and sea lions as well as dolphins. The walls were smooth concrete. Our object was to measure dolphin echolocation signals, and both reverberation and isolation presented serious problems. A wood lining which is echo suppressing in the frequency range of 10–150 kHz was developed and installed. The lining was constructed in 6‐ft square curtain panels, which were made up from small (3.5 × 7 × 2.5‐in.) blocks. This built‐up construction was necessitated by the particular grain orientation and pressure treatment of the wood required. The development of a satisfactory surface configuration and grain orientation was carried out in a small laboratory tank using 12‐in. square panels. Echo‐reduction measurements made in the USRD Lake Facility on full‐size panels and in the dolphin tank on the completed lining are in good agreement with the small‐tank data and show about 15–30 dB echo reduction over the entire frequency range. Transmission loss increases from about 15 dB at 10 kHz to 40 dB at the high frequencies.