This paper explores China’s longstanding geopolitical and economic interests in South East Asia, especially so from the nineteen-nineties onwards as China became more developed, and discusses their associated environmental impacts. In particular, two water bodies are examined, namely the Mekong River and South China Sea. Whilst Beijing’s spending on hydropower and navigation projects in the lower Mekong basin in mainland Southeast Asia, and large scale land reclamation of disputed insular features in the South China Sea may have benefited the Chinese state and its private sectors strategically, it has had, and will continue to also result in largely detrimental transboundary environmental impacts for Southeast Asian nations. The environmental consequences are of increasing regional concern for China’s southern neighbours, particularly at the local community level. With new grand international plans (such as the Belt and Road Initiative) and regional campaigns (such as Lancang-Mekong Cooperation), infrastructural advances would intensify. Hence, urgent attention should be given to how South East Asia responds to China’s grandiose plans on the ground in various ways from local to regional levels in addressing environmental concerns and reducing harmful environmental impacts. This paper identifies some ways to do so, and consider these measures in light of managing the extent of economic reliance on China and public Sinophobic sentiments, which would lead to adaptive engagement with China bilaterally and regionally.