The jelly-like substance has been found at the RSPB Ham Wall Nature reserve in Somerset. As yet the mystery slime has not been identified.
Steve Hughes, the RSPB site manager at Ham Wall, said: "This past week we've been finding piles of this translucent jelly dotted around the reserve.
"Always on grass banks away from the water's edge. They are usually about 10cm (4in) in diameter. We've asked experts what it might be, but as yet no one is really sure. Whatever it is, it's very weird."
Scientific speculation as to the nature of the jelly is varied.
One of the more favoured explanations is that it is a form of cyanobacteria called Nostoc.
Some, however, suggest that it is the remains of the regurgitated innards of amphibians such as frogs and toads and of their spawn.
Alternatively, it may be related to the intriguingly named crystal brain fungus.
Tony Whitehead, an RSPB spokesman for the South West, said: "Although we don't know what it actually is, similar substances have been described previously.
"In records dating back to the 14th Century it's known variously as star jelly, astral jelly or astromyxin. In folklore it is said to be deposited in the wake of meteor showers."
Mr Whitehead added: "It's great that in this day and age that there are still mysteries out there. We've read a few articles now and much speculation.
"One suggested it was neither animal nor plant, and another that it didn't contain DNA, although it does give the appearance of something 'living'.
"Our reserve team will be looking out for the slime over the next few days, but if anyone can offer any explanations we'd be glad to hear."
The public are being warned not to touch the mystery substance, and to inform nature reserve staff.
