Mystery continues to surround the reason more than 50 fish were found dead and dogs and a child became unwell on the River Spey.
It is feared some kind of pollution incident or chemical spill in the water caused the environmental concerns.
However, Sepa says visual inspections from officials have found no sign of sewage, fungus, smell or foaming that might suggest a leak or spillage has occurred.
Nearly two weeks on from the first reports, the government agency is still to draw definite conclusions from tests being done on water samples taken from the Spey.
Meanwhile, a range of factors remain under consideration for causing the deaths.
Sightings of dead fish on River Spey continue
Anglers have reported salmon and sea trout being “burnt” and “suffocated” over the last two weeks.
The first concerns about dead fish on the River Spey were reported on Saturday, September 9 and have stretched from Aviemore to Boat o’ Brig, slightly downstream from Rothes.
More sightings continued to be reported last week as Sepa and the Scottish Government’s Fish Health Inspectorate were notified.
The Spey Fishery Board has been alerted to more concerns this week but in reduced numbers.
Fishery board director Roger Knight explained the most recent dead fish appeared to have died several days ago.
He added: “I suspect that if it was an isolated pollution incident, which we can’t confirm, then it looks to have been flushed out very quickly.
“The river went into full spate after some heavy rain on Monday. It was still quite high yesterday but has dropped a little now.
“We’ve had a few more reports of dead fish being found but they don’t look like new fish that have died, they’re most likely from the incident last week and are being found now with the rise in water.”
The Spey Fishery Board has also reported no distilleries have raised water quality concerns in the last two weeks.
Sepa investigation continues
Officials from Sepa have monitored the temperature of the water, checked its pH and have also visited water treatment centres.
None of the checks so have revealed any obvious cause for concern, despite the number of dead fish in the river.
However, some test results are still outstanding as specialists attempt to find any clue as to the source of the potential pollution.
Sepa says the initial reports it received indicated the water quality was “abnormal”, but tests the agency has done itself have shown otherwise.
A spokeswoman said: “Officers checked historical water quality monitoring for comparison, inspected the river, and carried out bankside analysis of water samples.
“Both the supplied water quality reading and all subsequent results were found to be within expected ranges.
“Officers also contacted a number of regulated sites in the area and did not identify any potential cause of the reported fish mortalities, nor any evidence of impacts to water quality.
“A Sepa ecologist was undertaking routine ecological surveys on the River Spey during the period when dead fish were observed, and initial findings confirm invertebrate populations appear to be normal, giving no indication of any water quality issues.
“Any acute significant pollution in the river would also cause mortality in many other species and across the entire size and age range of fish.
“A number of other potential causes are being considered such as low oxygen in the water caused by low flows and high temperatures, as was the case at the time in the river.”
Anyone who has pollution concerns or has information about fish deaths on the River Spey should call Sepa’s pollution hotline on 0800 80 70 60.