Fast time-varying, phase variation, and Doppler shift constitute the features of the underwater acoustic (UWA) communication channel. As a consequence, the effect of intercarrier interference (ICI) becomes significantly critical for orthogonal frequency division multiplexing (OFDM) based UWA communication systems. In this paper, an ICI countermeasure, termed two-path transmission, is proposed. The key idea is to employ data repetition within two concatenated OFDM blocks according to subcarrier mirror mapping criterion. Through theoretical analysis and numerical results, it is shown that the proposed two-path transmission schemes can effectively improve the carrier-to-interference power ratio (CIR) in the presence of carrier frequency offset (CFO) and additive white Gaussian noise (AWGN). Furthermore, a recent sea experiment conducted in Taiwan in May 2013 verifies the ICI suppression capability of the proposed schemes in UWA channels.