You might think it a bit silly to cut a large hole through a concrete tank and then fill it with water but that is what happened at a large, prestigious water park during construction a few years back. The hole was to allow a pipe to be inserted but was cut in the wrong place and then forgotten until the tank was filled. The engineers concerned were both embarrassed that it had occurred and desperate to have the problem fixed.
Luckily for them the experts in concrete repair (us) were able to make good the damage in double quick time with a special water resistant mortar and fillers. The water park opened on time and still operates today after more than 10 years.
We are not saying where it is to protect those involved from further embarrassment.