Blood leakage

Bright blood means it is fresh, most likely it comes from physical damage, like tearing.
I do not know what you doing, but significant physical exertion and muscle tension combined with blood pressure spike of being in a cold shower can lead to small blood vessel rupture.
Pay close attention to what happens next, if you have sharp pain while peeing that does not diminish in the next 24 hours or you continue to have blood in urine - visit a doctor, do not play games.

As a side note, if you played with sounding devices - take this seriously, significant damage can be done to bladder sphincter and result in massive problems you will regret for the rest of your life.
Infection will seem like a joke if god forbid you develop urine retention problems.
I do not know if you were sounding, but if you did - take this as a lesson and think hard about this.
These types of injuries usually heal in few days, and there is high chance you may get an infection. If you get burning, discomfort or dull pain in your lower back, in the next few days, you most likely have a UTI and will need antibiotics, in that case do not play games go to the doctor.
But lets hope this was just something out of the blue