This research paper presents an investigation on an assessment of wave energy and resources in finite water depths for those historic and ongoing wave measurements which have been given in the forms of scatter diagrams or of wave (significant) heights and statistical wave periods, without the detailed spectrum information being available for analysis. As a result of such simplified wave statistical parameters, the assessment of the effects of water depths on wave energy and resources becomes difficult or inaccurate, because the effects of water depths are generally ignored and the formulas for deepwater waves are opted. From this research, it is shown that the formulas of deep-water waves may under-estimate the wave energy by up to 15% in irregular waves in the cases of finite water depths. To improve the wave energy assessment for those simplified historical wave data in finite water depths, a method is proposed for approximating the effect of water depth on wave energy calculation. The examples in the study show that the proposed method can reduce the errors of wave energy assessment to less than 5% for the individual sea/wave states, and less than 4% for wave energy resource in the cases of finite water depths.