The small pond at dawn really does look like 'half an acre of square pond opened like a mirror.'
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From 《观书有感·其一》 by 朱熹 (Zhu Xi, Southern Song, leading Neo-Confucian): '半亩方塘一鉴开，天光云影共徘徊。问渠那得清如许？为有源头活水来.' The poem's 活水 ('living water') has become shorthand for fresh input keeping the mind clear.
usage
鉴 (jiàn) here = 'bronze mirror' (ancient polished-metal mirror), not 'to inspect.' Same character, noun sense.
