Utility-scale projects for hydrokinetic energy extraction from rivers, tidal or ocean currents could include tens to hundreds of turbines in densely-packed hydro farms. The aim of the present paper is to obtain a better understanding of the power production and wakes generated by several devices modeling a straight array of horizontal-axis water turbines in a hydro farm. To accomplish this, stereo particle image velocimetry experiments were carried out to measure the flow properties upstream and downstream of the devices in the array including up to four elements. The study also provides measured values of power and thrust coefficients of the model turbines using strain gauges installed directly on the rotor shaft. The current laboratory experiments provide data on the efficiency of water turbines in arrays or in a hydro farm arranged in a single line.