This was an appeal from the Trial Division decision dismissing the appellants’ application for judicial review of a decision of Parks Canada with respect to an environmental assessment of a proposal submitted to it by Canadian Pacific Hotels (CP) to develop a meeting facility at the Chateau Lake Louise in Banff National Park. Parks Canada had concluded that the project was not likely to have a significant environmental impact provided that the mitigation measures associated with the project were implemented. The two appellants launched a judicial review application, which the Trial Judge dismissed without particularizing the standard of review to be used. The Federal Court of Appeal held that the appeal should be dismissed. It was of the view that the appropriate standard of review for discretionary decisions of substance pursuant to the authority granted in the Canadian Environmental Assessment Act was reasonableness, particularly because there was no privative clause, and because the level of expertise in administering the Act was minimal. The final decision incorporated the various notes and documents prepared throughout the decision-making process. To comply with the Act, the decision was required neither to be a model of legal analysis nor to consider fanciful projects by imagined parties producing hypothetical effects. The Court emphasized that the Canadian Environmental Assessment Act was not intended to eliminate any and all development in the national parks. One of its stated purposes was to ensure sustainable development. Neither was the Act intended to provide a rigid structure for conducting environmental assessments, as each set of circumstances required a different type of assessment, different scoping and different factors to be taken into consideration. While the Court had to ensure that the steps in the Act were followed, it had to defer to the responsible authorities in their substantive determinations as to scope of the project, the extent of the screening and the assessment of the cumulative effects in the light of the mitigating factors proposed. It was not for judges to decide what projects were to be authorized, but for the responsible authorities, provided they followed the statutory process.