I saw many dead fish when I was wandering at Bohai Park, and it makes me very sad.

这句话的时态不太一致。因为 "I saw" 是过去式，而 "it makes" 是现在时。正确的表达应该是： "I saw many dead fish when I was wandering at Bohai Park, and it made me very sad." 注意，"fish" 是复数形式，因此不需要加 "s"。另外，“wonder” 应该改为 “wander”，表示“漫步、闲逛”的意思。