Drug ‘zombies’ are being found lying on shop floors and slumped in phone boxes every day in this city centre.
Business owners in Lincoln say the drug users, who are normally young white men, are high on former ‘legal drugs’ like Spice and Mamba.
One businessman compared them to characters in a horror TV show, saying it is ‘like watching the Walking Dead’.
Some who start work early say they are afraid of being approached by people who have taken highly-addictive Spice, which can leave users in aggressive or catatonic states.
Lincoln was the first city to introduce a ban on legal highs back in April 2015, but many traders close to City Square say the problem is getting progressively worse.
Caylie Drinkall was opening up her café in the early morning when a man came in asking for a drink.
She said: ‘He was served by a member of staff and he seemed fairly normal. He went outside to drink his tea and then he came back in a totally different person.
‘He was aggressive towards staff and talking to different voices that he could hear. He then just passed out on one of the seats and fell on the floor.
‘He had bags of shopping, a wad of cash, bank cards and his drugs on the table.’
Ms Drinkall now fears unless immediate action is taken the problem will only continue to escalate.
She added: ‘If nothing is done now, in four or five years Lincoln’s streets will be flooded with people with mental and physiological health problems. It needs nipping in the bud.’
Debra Swain, owner of Riverside Café on Waterside South, compared the users to ‘zombies’.
She said: ‘I have never had an incident in the café, but it is very scary in the mornings, especially when there is nobody in the café.
‘They are like zombies walking around. Honestly, it is like watching The Walking Dead.
‘I get here in the mornings at around 5am when it is pitch black. I am a just a woman on my own. It can be intimidating. Sometimes I lock myself in.
‘They ask my customers for change and tea. Somebody has to do something or someone is going to end up dead.’
The county’s police force has acknowledged there is a problem and is vowing is to clampdown on people caught taking legal highs such as Spice.
But there is confusion about who is responsible for dealing with people who may have committed a criminal offence, but may also have health or mental health problems.
East Midlands Ambulance Service (EMAS) say it would be very difficult to pinpoint exactly how many call-outs they get related to legal highs.
However, the service has issued a warning to the public about taking such substances.