Local residents are demanding action about the mountains of rubbish and antisocial behaviour but there's another aspect to the park which is causing concern.
There's been an increase in people taking a dip since swimming pools were closed due to Covid restrictions but the council says while it looks tempting, the water is unclean, deep and cold.
For many years, it was a boating lake but now outdoor swimmers bathe there all year round.
They say it's time for a new approach and believe the council will never be able to stop people going into the water so it should educate them on how to swim safely.
Owen Hayman coordinates social media for Sheffield Outdoor Plungers, is a member of the Outdoor Swimming Society and has been enjoying the water at Crookes Valley for five years.
He has been campaigning for recognised swimming access at the park for several years. "I've tried to get the council on board to recognise the benefits of free swimming and provide helpful water safety signage but so far no progress," he says.
"I was at the park last weekend for a swim and it was exceptionally busy due to the football, end of university exams and great weather.
"There were drunk people in the water using inflatables, and unsupervised children jumping in, some of which looked like they were not confident swimmers.
"Three life rings had been abandoned in the lake, used as toys. This is very distressing to see, as lives were at risk.
"The standard blanket message from the council and South Yorkshire Fire and Rescue of "No Swimming" advice is completely out of touch and frankly useless in keeping people safe.
"People need good helpful advice that recognises the benefits of swimming while giving them the knowledge they need to make safe decisions.
"The council is simply burying its head in the sand, instead of seeing the potential to save lives while benefiting public health by supporting this free outdoor swimming."
Owen believes the lake is a safe place to swim. He adds: "The actual depth is irrelevant, once it's too deep to stand up, it doesn't matter how deep it is.
"The thousands of sensible informed people who swim there will tell you how safe it is, provided you can actually swim and know how to behave in deep water that can be cold.
"The water quality is good, there are no currents, and generally no underwater hazards. Water temperature varies from 4 degrees celsius in winter to over 20 in summer. Swimming there is not illegal, just prohibited by the council. There is no law in place."
Sheffield Council disagrees and maintains the water is unsafe. It says it has considered whether open water swimming can be allowed, taking advice from South Yorkshire Fire and Rescue, the Water Safety Forum and Health and Safety officers.
Coun Alison Teal, executive member for parks and leisure, said: "This position was reviewed again recently by SYFR and it was agreed that it is not a suitable location for casual swimming.
“There are many risks that support this decision, including water quality and testing, the depth at around 30ft in the centre, unknown objects under the surface, cold water temperatures and very limited views from the main road that could delay reporting of incidents.
"These risks increase when people have been drinking and we strongly advise people in the park, at all times, to stay out of the water.
“I understand that it may look like a safe place to swim, but we do not want to give people that false impression. With the recent cases we have seen relating to accidents in open water we cannot stress enough the importance of keeping safe."
The council says it knows people like to swim outdoors and directs people to The Outdoor City website - and to Owen's Outdoor Swimming Society website - to find advice on how to do it safely.
It says warning signs are in place to remind people not to swim and park staff do advise people against it, but without a continuous presence on site it is difficult to prevent people entering the water.
Yorkshire Water have also issued a warning after several tragic water-related incidents across the UK, including a teenager who recently died in a Rotherham reservoir.
Emergency services were called to Ulley reservoir in Rotherham on Friday, May 28 at around 3pm after receiving reports that a teenage boy had got into difficulty in the water.
Sam Haycock sadly died despite gallant efforts from his friends to prevent him from drowning.
His death has been felt across the community, with people paying tribute and offering condolences to his family after the tragic incident.
Gaynor Craigie, head of land and property at Yorkshire Water, said: “As the weather warms up it is important visitors to our reservoirs are not tempted to get into the water to cool off.
"Sadly, we’ve seen recently the dangers water can pose and it is important visitors to our sites understand entering a reservoir can be dangerous."
Following an inspection by SYFR, more signs and safety equipment has been ordered for Crookes Valley Park to reinforce the message plus additional throw lines and extendable reach poles are accessible by ringing 999.
Indoor pools are set to reopen fully this weekend so some bathers may switch back to lane and leisure swims. But when the weather is hot, the lure of Crookes Valley will be hard to resist for many.