I also came up with 2011 to be the 20th year.
See below.

Harbour lights began 1991
First year anniversary 1992
2nd year anniversary 1993
3rd year anniversary 1994
4th year anniversary 1995
5tht year anniversary 1996
6th year anniversary 1997
7th year anniversary 1998
8th year anniversary 1999
9th year anniversary 2000
10th year anniversary 2001
11th year anniversary 2002
12th year anniversary 2003
13th year anniversary 2004
14th year anniversary 2005
15th year anniversary 2006
16th year anniversary 2007
17th year anniversary 2008
18th year anniversary 2009
19th year anniversary 2010
20th year anniversary 2011