If you complete the run properly, your clothing will end up wet and covered in mud. That is why it is important to keep your body as warm and dry as possible.
Tight clothing will ensure that you don’t get caught on anything but will also mean you feel less resistance when swimming. It will also make running with wet clothing easier. If you also wear breathable clothing, it will dry quicker.
Your long or short running trousers may be ideal but don’t forget the obstacles you’ll be tackling along the way., Long trousers are more likely to prevent scrapes and grazes.