Foul smelling urine can be caused by a number of different things.
Some things that can cause foul smelling urine are overactive bladder, bladder infection, urinary tract infection and even some foods such as asparagus can cause your urine to have a foul smell to it.
If you're a woman you may have bacteria in your vagina that could be causing the foul smelling urine so if the foul smelling urine doesn't go away within a few days to a week then I would recommend going to the doctor and getting tested to find out the exact cause of the foul smelling urine.
If the foul smelling urine goes away within a week then it's likely just something you ate or something less serious.
Urinary tract infections are the most common cause of foul smelling urine which can sometimes make your urine smell more like fish.