Can you swim in a pool with algae?

Can I swim in my pool if it has algae?

Not until it is cleared and the readings in the table are back in range. The health departments do not treat green water as a cosmetic problem, because of what it says about the chlorine.

SA Health’s guidance for home pools puts it plainly: in pools disinfected with chlorine, the presence of algae is an indicator that free chlorine is not being properly maintained. It also lists when a domestic pool should not be used at all: when the disinfectant level or pH is outside the recommended range, when the water is dirty or cloudy, when it has been heavily contaminated, and when the pumps and filters are not working properly. A pool with visible algae usually fails two of those at once.

The risk is the germs that low chlorine lets survive, not only the algae. SA Health says contact with water contaminated with microorganisms may lead to infections of the skin, ears, eyes, central nervous system or digestive system. Queensland Health lists blue-green algae among organisms that flourish if introduced into poorly disinfected pools, and NSW Health’s 2026 guidelines note that some blue-green algae produce toxins.

There is a drowning reason too. NSW Health’s public-pool advisory document says it is essential to see the bottom of a pool clearly to detect a submerged or drowning person, particularly a child. In green water you cannot.

The swim-or-wait rule: if you cannot see the floor at the deep end, or free chlorine is under 1 mg/L, nobody swims, whatever colour the water is.

How long after shocking a pool can you swim?

SA Health’s shock-dosing instructions for home pools are the clearest published figures:

1. Add enough chlorine to reach 10 mg/L free chlorine: 200 mL of liquid sodium hypochlorite (12.5% available chlorine) or 30 g of granular calcium hypochlorite per 1,000 litres.
2. Hold 10 mg/L for at least one hour, with the pump and filter running the whole time.
3. Do not use the pool until free chlorine falls to 4 mg/L. SA Health says this may require leaving it overnight.

Worked for a 50,000 L pool: 200 mL × 50 = 10 litres of 12.5% liquid chlorine, or 30 g × 50 = 1.5 kg of granular calcium hypochlorite. A heavy bloom uses chlorine up, so test after the hour with a kit that reads that high, and top up if it has fallen below 10.

HealthyWA adds a separate floor for any chemical: never add chemicals while people are in the water, and allow at least 30 minutes for them to dissolve before anyone gets in. Thirty minutes is the minimum after a routine dose, not after a shock.

For comparison, public pools in NSW and Queensland must stay at or below 10 mg/L total chlorine, and NSW Health says shock dosing must only happen when the pool is closed. If someone in the household has had Cryptosporidium, SA Health’s process is different: 10 mg/L held for at least 25.5 hours, then another day or two before the pool is used.

Clearing algae before anyone swims

The method from the health departments is short:

• Bring chlorine and pH into range. SA Health: if algae is present, ensure disinfectant and pH levels are within the recommended range.
• Brush the walls and floor with nobody in the pool. Queensland Health’s public-pool troubleshooting table says to brush or vacuum off algae without bathers present, increase the disinfectant level and backwash.
• Vacuum the next day. HealthyWA: vacuum the settled algae from the floor the next day, and do not try to remove it by running the filter.
• Re-check the balance. HealthyWA says check total alkalinity, pH and calcium hardness before you allow anyone to swim.

Which half of the problem you are in, low chlorine or chlorine that is present but not working, is decided by one test, and why a pool goes green sets out that test and its causes; this page does not repeat them. If the water is milky rather than green, see why a pool goes cloudy.

Algae is cleared when the floor is visible from the side, the chlorine has held in range for a day, and the walls no longer feel slimy.

When algae keeps coming back: pump, filter or chlorinator

A pool that turns green again within days of being cleared usually has an equipment cause. SA Health and HealthyWA both say the filter should process the whole pool volume in 6 to 8 hours; for a 50,000 L pool that is about 104 litres a minute for 8 hours. HealthyWA also says some domestic salt chlorinators cannot make enough chlorine during heavy use.

So check, in order: pump hours (how long a pool pump should run), the filter (the turnover test for pool filters), and the chlorinator (why a chlorinator stops making chlorine).

If the answer is replacement equipment, ask for the pump, filter and chlorinator by model and flow rating, then compare pool quotes so the specification can be checked against your pool’s volume.

Common questions

Sources

• SA Health: Pools at home and maintaining them (free chlorine 1.0–3.0 mg/L; pH 7.2–7.6; shock dosing to 10 mg/L for one hour, 200 mL of 12.5% sodium hypochlorite or 30 g calcium hypochlorite per 1,000 L; do not use until 4 mg/L; algae indicates free chlorine not maintained; when not to use a domestic pool; Cryptosporidium 25.5 hours)
• HealthyWA: Swimming pools and spas (stabilised outdoor pools at least 2 mg/L below 26°C, 3 mg/L above; pH 7.2–7.8; 30 minutes after chemicals; brush, then vacuum settled algae the next day; filter in 6–8 hours)
• NSW Health: Guidelines for Managing Water Quality in Public Swimming Pools and Spa Pools, 2026 (total chlorine max 10.0 mg/L; shock dosing only when the pool is closed; blue-green algae toxins)
• NSW Health: Public Swimming Pool and Spa Pool Advisory Document, 2013, superseded by the 2026 guidelines (clarity: features on the pool bottom at its greatest depth clearly visible from the side; seeing the bottom to detect drowning people)
• Queensland Health: Water quality guidelines for public aquatic facilities, December 2019 (Table A2.1 total chlorine max 10 mg/L; troubleshooting: brush or vacuum off algae without bathers; blue-green algae in poorly disinfected facilities)

General information only, current at 2026-10-16. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.