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The 70-year-olds are in Oamaru this week for the South Island chartered clubs women's fours tournament, which started on Monday at the Awamoa, Phoenix and Meadowbank Bowling Clubs.
They are among 172 players who make up the 43 teams at the tournament, being staged for the 28th time.
Mrs Watson and Mrs Johnson both play for the Allenton Bowling Club in Ashburton.
With 12 years' experience under her belt, Mrs Watson has six years on her sister.
The pair have played with and against each other a lot and both enjoy the friendly rivalry that comes with being twin sisters.
"Oh hell yes," Mrs Watson said when asked if they enjoyed competing with and against one another.
"I am usually the skip and Rose is the lead. She doesn't take a blind bit of notice of me, but we do like to see each other do well."
That sibling rivalry extends to golf, a sport they have enjoyed for many years.
Both are also avid rugby fans - Mrs Watson is firmly in the Crusaders camp and Mrs Johnson is a staunch Highlanders supporter.
Even the bowls they use are rugby-themed.
Mrs Johnson's blue bowls feature the Highlanders logo and Mrs Watson's red bowls a knight on a horse.
"We're rugby nuts - any sport really," Mrs Watson said.
Mrs Johnson said they loved bowls because of the "camaraderie and friendship" the sport offered.
The top 16 championship and plate rounds and the bottom 11 consolation round were played yesterday.
The semifinals and final will be played today, as will the consolation semifinals and final, at at the Phoenix club and Awamoa club respectively.