Outdoor or indoor? Temp of water? I teach swimming lessons (I have for 20 years), and I typically start taking my kiddos in the pool (indoor mostly here in WA state) between the 6-8 week mark. We only stay in until baby starts getting cold. Sometimes that's 15 min, sometimes that's 45 min. Pools are typically 84-89 degrees with 86 being the norm. If it's an outdoor pool be careful of sun exposure.