Hello

I had this problem too, I have a ati card.
I changed particles\ funnelsmoke\ waterReflection Frustrumtest, was False
to True, and so far I have not seen oil spots or standing slicks and smoke balls any more.( I was wrong)!! Maybe this Frustrumtest thing should be true?

Needs more testing I think.
Hope this helps

P.S I played tutorial mission were you sink tree ship as a test, and I had tree oil slicks from tree sunked ships following my u-boat.

did another tutorial mission and it was 3 oil slick following my uboat.
P.S2 I finally rid my game of these evil oil spots.

I deleted 19particlegenerator-byte 6591 in TDW_FXU_Slicks_and_Spots_Particles, and made a copy of 560 particle generator in particles.dat and changed life time to 600, and used it in stead of "19particlegenerator-byte 6591". With these changes. evil oil spots (souls of the dead seamen?

) do rise up from the sea but they die soon. You hardly notice them any more.