In 1971 engineers and workers completed the Aswan High Dam, nearly 600 miles upriver from Cairo toward the Sudanese frontier.
这里:nearly 600 miles upriver from Cairo toward the Sudanese frontier的参考译文为“这座水坝在从开罗沿尼罗河向苏丹边境走去将近六百英里远的地方。”
请问为什么译文中没有体现upriver的含义?