The cause of an outbreak of the cryptosporidium bug in a leisure centre which led to 106 cases of the illness has been identified by an investigation.
An outbreak control team launched the investigation after reports of illness in children and adults who swam at the Merthyr Tydfil centre last August.
It was the result of a faecal accident on a children's slide.
Officials said it was important people with diarrhoea did not go swimming.
A total of 45 cases of the illness were confirmed through laboratory testing and the pool was closed for three weeks following the confirmation of the outbreak.
The outbreak control team was made up of professionals from Public Health Wales and environmental health officials from Merthyr Tydfil and Rhondda Cynon Taf councils.
Their report (this opens as a word document) concludes the cryptosporidium was introduced into the pool via the smearing of faeces on the leisure centre's toddler slide on 22 August, 2009.
It also said "gaps and weaknesses in policies and operational procedures and non-adherence to procedures in relation to incidents such as faecal accidents are also likely to have contributed to spreading cryptosporidium contamination widely at the time".
It makes a number of recommendations with the aim of reducing the risk of other outbreaks and highlights the role swimmers play in maintaining good pool hygiene.
One of the recommendations is that consideration should be given to making features that are likely to need frequent cleaning, like toddler slides, removable to reduce the possibility of contamination accidentally entering pool water during cleaning.
Dr Gwen Lowe, consultant in communicable disease control for Public Health Wales, chair of the outbreak control team, said: "This outbreak demonstrates how important it is that people who are suffering from diarrhoea, or who have had it within the last 48 hours, should not go swimming.
"If they have been diagnosed with cryptosporidium they should not swim for two weeks after their symptoms have settled.
"I would also take this opportunity to urge parents to ensure that their children have clean hands and clean bottoms before going swimming."