我今天去海滩游泳

Agree with Gavin on the proposed change: 我今天去海滩游泳 (it's usual to put time and place before action, and 去一个地方做一个动作 is fairly common). Note that if this was 'oral chinese', which is less strict on the ordering, your original sentence would be understood without issue (it's common, when talking, to not put all the sentence elements in the "correct" order, because we aren't sure what we want to say or something :P)

I think maybe "qù xyz", is to "go somewhere", not to "go something".... but I'm no expert haha, I could be wrong maybe Wǒ jīntiān qù hǎi tān yóuyǒng ?