Ariarne Titmus' overwhelming emotion is relief.

The Australian swim star's Paris Olympics are over. And so is the suffocating pressure.

"I knew what to expect physically coming into this, from learning from the last Olympics," Titmus said.

"But emotionally this week, I had so much expectation on me the past few years to go back-to-back and continue my winning streak internationally the 400 (metre freestyle) especially.

"And you kind of put that in a little box and put it in the corner and don't really recognise it.

"And I am so good at putting that pressure in a little pile and using it to my advantage to race.

"But then when it's off your back, somehow it creeps out and just explodes.

"And I'm feeling the most unbelievable sense of relief now that I'm done."

Titmus' Games end with two gold medals and two silvers, adding to her collection from Tokyo three years ago of two gold, one silver and a bronze.

In Paris, the 23-year-old successfully defended her 400m freestyle crown and was the anchor in Australia's triumphant women's 4x200m relay.

Titmus' silver in the 800m freestyle behind American great Katie Ledecky on Saturday night followed silver in the 200m freestyle, won by compatriot and swim club-mate Mollie O'Callaghan.

"I'm so proud of my efforts this week," she said,

"Two gold, two silver, I couldn't defend my 200 but certainly happy that it was my training partner that won it and to be second to her is great.

"I'm just so happy with my week.

"But I can't wait for a big rest."

Titmus' campaign finished with an 800m freestyle match race against American hero Ledecky, now an eight-time Olympic gold medallist.

Ledecky has won the event at an astonishing four consecutive Games dating back to London 2012.

Titmus watched that race as a year six school student.

"I hadn't even been to my first age nationals in Australia, I was in grade six," she said.

Titmus watched Ledecky win again in 2016 in Rio.

"I remember watching her in Rio win in eight minutes and four (seconds)," she said.

"At the same time I was in Hawaii at junior Pan-Pacs racing. And I was an eight (minutes) 37 (seconds) swimmer.

'And eight years later, I challenged her ... it's pretty cool.

"I'm really proud of myself and I feel very honoured and privileged to be her rival and I hope I've made her a better athlete - she certainly made me become the athlete I am."

At the Tokyo Olympics three years ago, Titmus took silver behind Ledecky, as in Paris.

"This is the toughest week of racing you can possibly do," Titmus said.

"I gave it everything. I said to myself I wouldn't sleep at night if I felt like I left anything out there.

"I'm so proud of my efforts. I took it to her (Ledecky), I challenged her and I made it a great race and I gave it everything.

"She just had an extra bit in the legs at the end but she's an absolute champion.

"I know how hard it is to defend a title.

"It's so much harder to win a second time. And to be on top for over 12 years is unbelievable."