This paper presents results from a propagation measurement campaign carried out in the Trondheim harbour during the period from June to November 2007. Two vertically mounted transducers operating at a carrier frequency of 38 kHz permitted both single-input/single-output (SISO) and multiple-input/multiple-output (MIMO) channel measurements. The upper transducers at both sides were mounted around 2 meters from the sea surface. The sound velocity profile measurements showed large variations in the upper layers of the water column during the campaign period. Due to the fixed mechanical transducer constructions, the observed Doppler spread was low. The Delay spread however varied from 0.5 ms in the summer up to 9 ms in November. The calculated spatial multiplexing capacity within a 3 kHz bandwidth of the MIMO topology gave a factor in the order of 1.8 capacity improvement compared to derived SISO capabilities. The reference SISO propagation channels used in the calculations were one of the estimated elements of the corresponding MIMO channel matrices. Channel state information (CSI) at the transmitter maximises the capacity, particularly at low signal to noise (SNR) rations. Simulations comparing capacities achieved with and without transmitter CSI are shown. The results show that for the observed channels, spatial multiplexing MIMO capacity outperforms SISO and verified that CSI is beneficial at decreasing SNR values.