The cache IS at the posted coordinates
However, this is a challenge cache. In order to sign this log you must complete the challenge first.

is·land /ˈīlənd/ noun. A piece of land surrounded by water.
10 UNIQUE ISLANDS
This is my first challenge cache.
Before I moved to Michigan, I was born and raised on an island. We have plenty of water here in the Great Lakes and there are many islands with caches. So the challenge is to have found at least one cache in 10 UNIQUE islands before signing the log. Since each of the 10 islands is unique, those hundreds of caches found on Belle Isle as part of any of the Belle Isle Geocaching events count as ONE island. Lots of islands here to chose from: Belle Isle, Gross Ile; Gull Island (Jobbie Nooner); Mackinaw island; Harsens Island; Manitou Islands; and if you are adventurous enough you can go all the way up to Isle Royale. There are lots of other un-named islands.
You must post the list of caches that you are using as qualifiers, the title of the caches, when you found them and what island are they located at. There are millions of islands in the World and these islands do not have to be in Michigan. Islands of all sizes count: whether it is the island-nation of Australia or this little no-name island behind Lakeside Mall in Sterling Heights or even smaller than that. Any size island counts as long as it is surrounded by WATER (ocean, river, lake, swamp, etc..) so no road traffic islands or temporary flooded parking lot lamp post skirt cache. Some islands will be accessible by boat, some islands will be accessible by swimming to it, other islands will be accessible by plane or by walking on a bridge to it.
Oh and this cache is, of course, located on an island. This challenge cache itself does not count towards the count but this island does count. So just go ahead and find another cache on this island if you want this island to count too. Past finds also count.
My Island Challenge caches:
GC5CM89 : Islands Challenge (10)
GC5CQTW : Islands Challenge (20)
GC5C7DB : Islands Challenge (30)
I will be trying for this challenge myself. This is what I have:
#1: GCYCG9 : Sweet Land of Liberty - 6/18/2010 - Little island behind Mall in Sterling Hts, MI
#2: GCPFP8 : Arch Rock - 9/4/2010 - Mackinaw Island, MI
#3: GC1WCDC : Gilligan's Island - 9/12/2010 - The island in Stoney Creek Metro Park, MI
#4: GC17VCE : tortuguero top - 12/26/2010 - The island of Puerto Rico
#5: GC257R1 : Parque de las Palomas - 1/6/2011 - The island of Old San Juan, Puerto Rico
#6: GC3A89Z : Belle Isle Pot Luck 2012 - 3/31/2012 - Belle Isle in Detroit, MI
#7: GC2XVTR : Le Suppositoire Inn de Montréal - 6/29/2013 - The island of Montréal, Canada.
#8: GC2JJ45 : Thunder Cove Sea Caves - 7/2/2013 - Prince Edward Island, Canada
#9: GC1GZ4V : Celtic Caching's North Star - 7/3/2013 - Cape Breton Island, Nova Scotia, Canada
#10: GCWJZ3 : Extreme East - 6/12/2006 - Newfoundland Island, Canada
#11: GC3RJ39 : The Bar That Named a Town - 7/9/2013 - Mt Desert Island, Acadia NP, Maine
#12: GC4D7F : The Empire Strikes Back - 7/11/2013 - Manhattan Island, New York
#13: GC25PJR : Lido Isle - 9/28/14 - Lido Isle, Newport Beach, California
****After the publish of this cache I updated my own island list with the following:
#14: GCGFJ4 : Lafitte's Blacksmith Shop - 6/22/15 - Île d'Orléans, Louisiana
#15: GC3FMHV : LA GROTTE NAPOLEON - 8/22/17 - Island of Corsica, France
#16: GC3VH0G : PALMA - 8/24/17 - Mallorca Island, Spain
#17: GC4TGCV : Every Picture Tells A Story - 8/25/17 - Island of Sardegna, Italy
#18: GC4GKEE : Le Lutétien de Notre-Dame - 6/29/18 - Ile de la Cité, Paris, France
#19: GC7BA4 : Death in Venice - 8/28/17 - Isola San Michele (Venice Cemetry), Venice, Italy
#20: GC7BFF : The Snail - 8/28/17 - An island in the San Marco region of Venice, Italy
#21: GC62RA5 : La Natura Delle Cause - 8/28/17 - Another island in San Marco, Venice, Italy
#22: GC5GYJR : Ponte della Salute - 8/28/17 - Yet Another island in San Marco, Venice, Italy
#23: GC42CTN : Orio's House - 8/28/17 - An island in the Castello region of Venice
#24: GC474AN : The anchors - 8/28/17 - Another island in the Castello region of Venice, Italy
#25: GC47068 : La statuina - 8/28/17 - An island in the Dorsoduro region of Venice, Italy
#26: GC31CKZ : par le sconte 03 - 8/28/17 - An island in the San Polo region of Venice, Italy
#27: GC473GN : The clock - 8/28/17 - Another island in the San Polo region of Venice, Italy
#28: GC4H2DB : Gondola ride - 8/28/17 - An island in the Cannaregio region of Venice, Italy
#29: GC24X6Q : The pollution in the Lagoon of Venice - 8/29/17 - Tronchetto Island, Venice, Italy
#30: GC7B8P8 : Brugge - The old Saint-John's Hospital - 7/1/18 - An island in Bruges, Belgium
#31: GC7B940 : ♥ Pont d’Amour ♥ - 7/1/18 - Another island in Bruges, Belgium
#32: GC5KWKP : Dam Square of Amsterdam - 7/2/18 - One of the 90 islands of Amsterdam
#33: GC5A7X0 : Bicycle Parking - 7/2/18 - Another of the 90 islands of Amsterdam
#34: GC1BA1Y : LINDAVIA-72 (Tret mich) - 7/5/18 - Lindau Island, Lindau, Germany
#35: GC2E34F : Island or not island ? - 7/9/18 - Island of Mt St Michele, France
#36: GC2AY4B : John Pennekamp State Park - 11/19/18 - Key Largo Island, Florida
