“据说在那个湖底发现了一个古城的遗迹”一句中从句中用was found,has been found还是had been

It is said that an ancient city ruins has been found at the bottom of the lake.
如果前面是 It is said ,是现在式 ,表示现在在讨论一个谣传,那就用has been found.
如果是叙述一种事情,当时用的是描述的方式,前面是 It was said ,是过去式 ,表示讲述的一个当时的谣传,那就用had been found.总之这个完成式要取决于前面句子的时态,只比前面用的差一个阶段就可以了.
如果还是不明白,

如果是“It is said that...”, 用“has been found”；
如果是“It was said that...”, 用“had been found”。
因为时态要一致！

我觉得如果用it is said的话，was found就行了；
对于it was said，要用到had been found，不过it was said似乎很少用到，不知道是不是我孤陋寡闻。。
所以我觉得用it is said + was found 可以表达清楚。