Urine that smells like fish is usually caused by something specific and fixable, but you should see a doctor or sexual health clinic if it keeps happening or comes with other symptoms like pain, discharge, or fever.

Why does my wee smell of fish?

Quick Scoop

A fishy smell in pee can come from several things, ranging from harmless (diet, vitamins) to issues that need treatment (UTI, vaginal infection, or rare metabolic problems).

1. Common, often harmless causes

  • What you’ve eaten
    Foods rich in choline (fish, eggs, some meats, dairy, Brussels sprouts, cabbage, asparagus) can make your wee smell stronger or fishy for a day or two.
  • Not drinking enough water
    When you’re dehydrated, your urine is more concentrated so any odor (including food- or vitamin-related) becomes much stronger.
  • Vitamins and supplements
    Some B vitamins (especially B6) and certain supplements can change urine odor and make it sharp or unusual.

If the smell started soon after a heavy fish/egg meal or new vitamins and goes away in a day or so, diet/supplements plus mild dehydration are very likely.

2. Infections that can cause fishy wee

Even though the smell comes from the pee, the source can be the bladder, urethra, or the vagina (in people with a vagina), and sometimes it all mixes together when you go to the toilet.

  • Urinary tract infection (UTI)
    • Symptoms can include burning when you pee, going more often, needing to pee urgently, cloudy pee, and strong or foul smell.
* Sometimes there is lower tummy or back pain, and occasionally fever or feeling generally unwell.
  • Bacterial vaginosis (BV) – if you have a vagina
    • Very common cause of a fishy smell around the toilet area.
* Often gives a thin, grey or yellow‑green discharge with a noticeable fishy odour, which you might smell more after sex or around your period.

* The discharge can mix with urine, so it can seem like “wee smells like fish.”
  • Sexually transmitted infections (STIs)
    • Trichomoniasis and some other STIs can cause discharge and a fishy or foul odour, sometimes with itching, soreness, or pain when peeing or during sex.

Any new fishy smell plus discharge, itching, burning, or pelvic pain should be checked by a GP, gynaecologist, or sexual health clinic.

3. Rare but important causes (fish‑odor syndrome & others)

  • Trimethylaminuria (“fish‑odour syndrome”)
    • A rare metabolic condition where the body can’t properly break down a compound called trimethylamine (TMA), which smells like rotten fish.
* The smell can come from sweat, breath, vaginal fluids, and urine; it often gets worse after eating fish, eggs, liver, beans, or other choline‑rich foods, and may be present from childhood or adolescence.
  • Other health issues
    • Advanced kidney or liver disease and some metabolic disorders can also change body and urine odour, though these usually come with other strong symptoms like fatigue, swelling, jaundice, or feeling very unwell.

4. When you should seek help urgently

You should get same‑day or urgent medical advice if:

  1. The fishy smell is strong and lasts more than a couple of days with no clear food/vitamin cause.
  1. You have burning when you pee, need to pee constantly, see blood in your urine, or have fever or side/back pain (possible UTI or kidney infection).
  1. You have vaginal or penile discharge, itching, soreness, or pain during sex (possible BV or STI).
  1. You feel very unwell, have tummy swelling, yellow skin/eyes, or major changes in urination (possible liver or kidney problems).

If you’re pregnant, immunocompromised, or have diabetes, you should be extra cautious and contact a doctor early for any new strong urine smell.

5. Simple steps you can try today

These don’t replace medical care, but they can help while you arrange an appointment:

  • Drink more water over the next 24–48 hours to dilute your urine.
  • Notice your recent diet (fish/eggs/strongly flavoured foods, new vitamins). If likely, cut them out briefly and see if smell fades.
  • If you have a vagina, avoid scented washes or douching; wash with plain water and mild, unscented products only on the outside.
  • Use condoms if you suspect any STI risk and get an STI screen.

Mini forum‑style recap

“why does my wee smell of fish?”
Often: what you ate, dehydration, or vitamins.

Sometimes: UTI, BV, or an STI.

Rarely: a genetic condition like trimethylaminuria or serious liver/kidney disease.

If this is new for you, has lasted more than a couple of days, or comes with any pain, discharge, or feeling unwell, it’s safest to book a GP or sexual health clinic visit and describe exactly what you’re noticing. Meta description (for SEO):
Fishy‑smelling urine can be caused by diet, dehydration, infections like UTIs or bacterial vaginosis, sexually transmitted infections, or rare conditions such as trimethylaminuria. Learn causes, signs, and when to see a doctor.

Information gathered from public forums or data available on the internet and portrayed here.