https://www.abc27.com/local-news/carlisle-west-shore/mandatory-water-conservation-order-in-effect-for-mechanicsburg-area/

 

An underground oil tank was found leaking diesel to the creek near me.  How will it affect the smallies and other fish in the creek? Also, how will it affect wadefishing anglers? How about the drinking water? Sorry I panicked a bit and made a Walmart run for bottled water.

It's hard to say.  It depends on how much oil leaked into how much water.  In low enough concentrations, the fish might survive.  But it's not healthy for any living creature, outside of a few microorganisms.  

think of it as pre-seasoning for all the fish that will be floating soon.

Diesel isn’t good for them, but at the same time it doesn’t mix with the water. It will get on the solid matter along the edges and absorb into some organic matter. If it’s small amounts that are leaked I wouldn’t expect much harm. If it’s all 9100 gallons then I would worry.