So I've got two female cats, a 1 year old and a 6 year old, and the younger one has such an ammonia stench to her pee that it's utterly noxious.
Common suggestions online are that the cat is dehydrated - which with two water fountains, wet food twice a day, and the sheer monsterous size of the pee clumps, is not the case. They've got three litter boxes which are scooped daily, so it's also not like we're leaving things to fester and grow more pungent. It's not a new development, her pee has always been really potent, so I'm also not thinking UTI.
I've tried sprinkling baking soda in the litter after scooping, which helps a bit with residual smells, but I'm looking for any suggestions to counter this constant ammonia assault.
The culprit:
Mirroring what others have said, see your vet! Kidney dysfunction is extremely common in cats, and as with most medical issues it's much, much better to address it early before it snowballs.
One possibility is that your cat is getting too much protein and her kidneys are struggling as a result. This is unusual (cats naturally need lots of protein), but not unheard of. When you visit your vet, make sure you discuss diet in detail.