Celebrations turned to upset when a wedding party had duck eggs thrown at them by yobs who had raided a nest.
Police are warning they will not tolerate antisocial behaviour after recent incidents in Durham last weekend.
Officers believe the trouble may be connected to the additional numbers of young people flocking to the city for the funfair currently in place at The Sands, which runs until Saturday, April 22.
In the first incident a wedding party at the Radisson Hotel was disrupted at about 5.30pm on Saturday by a large group of youths throwing duck eggs at party members and vehicles.
The eggs were partly developed and were presumably taken from a nest on the River Wear, which is in front of the hotel.
The following evening there was a large scale disturbance involving two groups of youths, again near to the Radisson, which resulted in at least one reported assault.
No arrests have been made at this stage in connection with either incident, but police inquiries are ongoing.
Sergeant Kay Howarth, from the city's neighbourhood policing team said; “We have raised our concerns with the organisers of the fair, who have taken on board various suggestions we have made.
"Police will not tolerate this sort of behaviour and over the next ten days while the fair is on, we will be carrying out extra patrols in the area around the Sands to nip this problem in the bud.
“The vast majority of people coming to the fair are simply out to have fun. By taking a firm line against anyone who misbehaves, we hope the atmosphere can stay positive and everyone can enjoy themselves.”