In March the Fuchun River is truly "spring-arrived river water, green as indigo".
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history
From Bai Juyi's (白居易, Tang dynasty) 《忆江南》其一: 江南好,风景旧曾谙。日出江花红胜火,春来江水绿如蓝。能不忆江南 — 'Jiangnan is good; its scenes I once knew well. At sunrise, river flowers are redder than fire; when spring comes, river water is greener than indigo. How can I not remember Jiangnan?' Bai Juyi's nostalgic look back at Hangzhou.
usage
Always cited with its twin line 日出江花红胜火. 蓝 here refers specifically to the indigo plant (Persicaria tinctoria) used for blue-green dye in Tang times — a darker, bluer green than the word suggests in modern Chinese.