She said there was often more than 20 vehicles and tents on the small reserve over summer, and the public toilets - which are also used to wash dishes and clothes - were overrun.
Mrs O'Shea said freedom campers have been spotted peeing into the estuary or off the bank, despite the toilets.
She said campers left their rubbish piled up between the bins. Once, she had a whole duvet stuffed in her rubbish bin.
In recent weeks, the residents have taken the bins away and Mrs O'Shea said it forced campers to take their rubbish with them.
Armourguard have been contracted to monitor the sites. Mrs O'Shea said often the officers would turn up at around 12pm and the campers have usually left by 10am.
In a letter of complaint to the council she suggested a portion of land within the Department of Conservation campground at Otamure Bay, about 4km north, be set aside to accommodate freedom campers in a more controlled environment.
Mrs O'Shea said other residents were fed up and had also complained to the council.
It comes as Whangarei Mayor Sheryl Mai and Far North Mayor John Carter joined other local mayors to meet with Minister of Tourism and Te Tai Tokerau MP Kelvin Davis in Wellington yesterday to discuss freedom camping.
Ms Mai said as a result of the meeting, a working group is being set up to look at solutions to the "many and varied" issues related to freedom camping around the country.
It would look into having consistent signs throughout the country, and reviewing the Freedom Camping Act.
Ms Mai said she could understand the frustration of the Whananaki residents and they raised valid concerns.
Mr Davis said freedom camping was a significant issue for many local authorities who faced significant stress and challenges with the seasonal influx of freedom campers.
"Freedom camping is a complex area. Freedom campers bring economic benefits to our regions, but the behaviour of a small percentage and the sheer increase in volume of freedom campers is causing real problems for some councils," Mr Davis said.
An interim report on freedom camping was presented to Whangarei District Council at a council meeting last month which outlined the number of complaints received between October 21 last year and January 29 this year.
Between Labour Weekend and Easter Weekend last year the council received 105 complaints, alongside 82 complaints from Labour Weekend to the end of January so far.
A full report on the summer monitoring and enforcement will be presented to the council in late April or early May. Residents' concerns would be part of that report.