The organisers of a popular cross-country event in the borders have apologised after rampaging runners killed dozens of frogs.

More than 1500 competitors on the Mighty Deerstalker fancy dress run plunged through two man-made ponds on the 10 kilometre course, wiping out colonies of frogs and spawn in the breeding grounds. Shocked spectators say they watched dozens of terrified amphibians attempt to leap for their lives from the stampede.

The organisers of the adventure race at Innerleithen in Peeblesshire have now vowed to carry out more stringent checks of the course next year, following fierce criticism from animal rights groups.

One eye witness, Christine McIntyre, said: "It was terrible. One minute the pond was calm but as soon as the first runner went through frogs started appearing from everywhere and they were all getting squashed.

"Some of the first runners also had spawn hanging off them. It spoiled a really good day for me and there were plenty others like me who thought it was terrible."

One of the fun runners added: "There were frogs in both ponds behind the car park and it was a case of trying not to stand on them as you came out.

"I couldn’t tell you how many were killed but there were quite a few at the second pond already squashed by the time I went through."

There is no legal protection for the common frog or its habitats under the Wildlife and Countryside Act of 1981 but cruelty officers believe more care should still have been taken.

Scottish SPCA Chief Superintendent Mike Flynn said: “The organisers of the event should have taken into account the likelihood that frogs would be present in the ponds and planned an alternative route as a result. We also don’t know whether there are any other protected species in the area that the race took place.

“We would advise organisers of such events to check with their local Scottish Natural Heritage officer whether any species of wildlife may be present in the area and should be avoided.”

The ponds were dug by the Forestry Commission around five years ago during upgrade work at the downhill mountain biking course where the race takes place. Over the past few years, plants and wildlife have taken up residence.

Course organiser Gary Tompsett said he had walked the Mighty Deerstalker route before last weekend’s event without seeing any frogs. He said: "I waded through both ponds and all I noticed was a really small amount of frog spawn in one corner.

"When we first started the race four years ago the ponds were new and looked manmade which was perfect for the race - but there is a lot of vegetation there now.

"I was told after the race that some frogs had been in the ponds but I genuinely didn’t know and I can only apologise. If I’d seen a lot of frogs when I waded through the ponds I would have changed the route.

"We will look at finding a solution for next year."