In the 1950s Ontario and New York built hydroelectric structures in the St. Lawrence River, while the federal governments of Canada and the United States constructed the St. Lawrence Seaway to work in conjunction with these power works. The engineering works that enabled this megaproject, approved by the International Joint Commission (IJC), were also designed to regulate water levels and flows on the upper St. Lawrence and Lake Ontario, and a method of regulation was established to set outflows, named Plan 1958-D. This paper covers the initial establishment of this regulation plan, identifying its weaknesses. Though the new water regime provided benefits for certain interests (primarily power, navigation and property owners), it could not always adequately cope with high and low water supplies into the system outside those originally anticipated. Moreover, as is shown, the creation of the St. Lawrence dual project and the connected method of regulation had a range of negative ecological impacts and harmed other interests – including the Mohawk groups in the territory that straddles the project area. By the late twentieth century, serious consideration was being given to replacing Plan 1958-D. This paper explores the technical study, negotiations and political intrigue that involved hundreds if not thousands of professionals, public servants, riparians and commercial interests in both countries that eventually led to a new method of regulation. On 6 December 2016 the governments of Canada and the United States formally gave concurrence to a revised Order of Approval from the IJC that replaced Plan 1958-D with Plan 2014. The rationale for these changes is explored, as well as the challenges faced by the IJC and its technical advisory groups, and the lessons that can be learned are identified.

1950年代，安大略省和纽约州在圣劳伦斯河上建造了水力发电设施，而加拿大和美国联邦政府则建造了圣劳伦斯河航道，以与这些发电站协同工作。由国际联合委员会（IJC）批准的，使该大型项目成为可能的工程设计，还旨在调节圣劳伦斯河和安大略湖上游的水位和流量，并建立了一种调节流出量的方法，命名为Plan 1958-D。本文涵盖了该法规计划的初步制定，并指出了其缺点。尽管新的供水制度为某些利益（主要是电力，航海和财产所有者）带来了好处，但它不能总是足够地应对超出原先预期的系统的高水位和低水位。而且，如图所示，圣劳伦斯双重项目的创建和相关的监管方法产生了一系列负面生态影响，并损害了其他利益，包括横跨项目区域的莫霍克族。到20世纪后期，人们已经开始认真考虑取代1958-D计划。本文探讨了技术研究，谈判和政治阴谋，涉及两国成百上千的专业人员，公务员，河岸居民和商业利益，最终导致了一种新的监管方法。2016年12月6日，加拿大和美国政府正式同意IJC的经修订的批准令，将1958-D计划替换为2014计划。探讨了这些变更的理由，