In a new video released on their Reactions channel, the ACS assures us that it's totally cool to go with the flow. First off, your urine is made up of 95% water — you know, that same stuff you're swimming in. And, the sodium and chloride ions found in pee are also a major component of seawater. So, you're not adding anything that isn't already there. Second, the nitrogen in urine combines with water to produce ammonium, which can feed ocean plants. And finally, the ocean is full of urine anyways; fish pee, too. A lot.
So, while you should continue the time-honored tradition of Not Peeing In The Pool Or In Protected Ocean Areas, feel free to go for it the next time you need to take a leak in the general sea.