"It should be a fun activity and a safe activity," says Ellie about a trip to the beach with her children.

Two weeks later, her three-year-old daughter began vomiting and spent five days in hospital after being diagnosed with Hepatitis A.

The Hampshire mother believes Violet picked up the infection during a family visit to Avon Beach in Dorset.

She is one of three families who say their children became seriously ill after spending time in and around Christchurch Harbour during the summer holidays.

Although the exact source of the infections is impossible to establish, the Environment Agency (EA) is carrying out additional inspections and sampling as it investigates concerns about water quality in the area.

At first Ellie, from Winchester, put it down to a childhood bug, but within days Violet's condition deteriorated and the whites of her eyes turned yellow.

The family took her to hospital where she says doctors realised something more serious was going on: "It was very quickly scaled up to this is a serious kind of emergency situation.

"My head immediately went to worst case scenario. It was terrifying."

Blood tests later confirmed Hepatitis A and Violet spent five days in hospital undergoing further investigations and treatment.

"It's not something I ever expected my child to be exposed to, especially in the UK where it is extremely rare," Ellie says.

Eight weeks later, her daughter continues to take medication and undergo blood tests.

Ellie says the experience had changed the way she feels about trips to the beach: "I don't want them to feel afraid of the water or afraid of playing in the sea.

"But I'm very conflicted about that because I also don't want them to go in the sea currently."

Aisling and her twin eight-year-old daughters are regular visitors to Avon Beach, just a short walk from their home.

So when Keeva swallowed a large amount of seawater after being hit by a wave while swimming, her mother was not especially concerned.

Four days later, Keeva was rushed to hospital after becoming increasingly lethargic, developing a high temperature and passing blood.

Aisling explains: "You're thinking all the worst things once your child gets sick. I just wanted her better and you're praying everything will be OK."

Doctors later diagnosed campylobacter, a bacterial infection commonly associated with food poisoning but which can also be passed through contaminated water.

Aisling believes Keeva's illness is connected to her time in the sea: "I don't think the emphasis is me needing to prove Keeva got sick from the sea.

"I think the emphasis is the Environment Agency and our council proving to us that our waters are safe."

More than two months later, she says she is still looking for answers from them: "I want for next summer to have some reassurances and some transparency. We need things to happen now."

The family of three-year-old Ivy, from Poole in Dorset, say their lives have been a "nightmare" since she was diagnosed with E. coli in August.

She has been readmitted to hospital several times since contracting the bacterial infection.

E. coli can be transmitted in a number of ways, including through contaminated food, contact with infected animals or contaminated water.

But Ivy's family believe she became ill after falling from a paddle-board in Mudeford, Dorset, during the summer holidays.

It is one of several cases that have emerged amid ongoing concerns about water quality in and around Christchurch Harbour.

A fundraising page set up to support the family says the have had to endure "more than any family should have to" in recent weeks.

The EA says it is carrying out inspections and bacterial sampling around Christchurch Harbour as part of its investigation into water quality concerns in the area.

The agency said it was also setting up joint monitoring with Christchurch Harbour and the Marine Society to track any changes in water quality in real time.

Meanwhile, the UK Health Security Agency (UKHSA) says cases of E. coli and campylobacter in Dorset were not above expected levels for the time of year.

Christchurch Harbour sits at the point where the Rivers Avon and Stour meet before flowing out to sea.

Oceanographer Dr Simon Boxall, from the University of Southampton, describes the shallow harbour as a "mixing basin", where river water combines with seawater before tides carry it out through the narrow entrance at Mudeford.

In theory, this process helps disperse material carried downstream, but Boxall believes the build-up of sand and mudbanks near the harbour entrance has significantly changed how water moves through the area.

He says: "Rather than just flow out, if you like, it's hitting some of these new banks and structures offshore that have built up naturally and it's pushing that water back in. It's giving us what we call a back eddy."

Boxall says this could direct water back towards Avon Beach and Hengistbury Head.

He believes this summer's unusually warm weather may also have been a factor, bringing more people into the water while creating conditions that can encourage the growth of some bacteria.

The Environment Agency say to date no specific source of pollution have been found.

The families say they may never know exactly how their children became ill, but they want monitoring to continue so people can make informed decisions about using Christchurch Harbour and its surrounding beaches.

If you have been affected by the issues in this story you can contact Jo Palmer via jo.palmer@bbc.co.uk