The San Marcos City Council proposed $1.2 million to repair Thompson’s Island after it was declared a Federal Disaster Area because of the 2013 Halloween Flood.  In August 2014 the San Marcos City Council approved $1 million to repair the dam that creates Thompson’s Island, just like they did at Rio Vista Park.  That is all a part of the public record, but what most don't know is what was here for centuries before our ancestors arrived.  The evidence is everywhere on the San Marcos River that travertine dams grew up as tall as their structures would support, and maintained the water levels in the ever flowing springs.  These "Dancing Waters," as the native Tonkawa Indians called them, are the natural flows of this calcium-rich, spring-fed river.  It appears that even our drought standards are relatively wet compared with most of the history of our area.  Without these travertine waterfalls the fish and wild rice could not have survived the droughts.  Even though travertine is a prized building material, just like the trees that used to fill our river, it is abundant and continues to grow all around Thompson's Island. Look for these beautiful flow stones growing on all of the walls of Thompson's Island, and the bridges above and below it, not to mention all of the ledges downstream! It will continue to grow so long as we have the pristine water here.  So, don't let anyone take away the water at the only San Marcos City river park in East San Marcos! Let's Save Thompson's Island not just for the endangered species, but for our children and future generations to enjoy. . .

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Clean water is the most precious resource that we have in Central Texas.  Thompson’s Island, San Marcos's newest park, holds about 1/3 of the surface area of the clean water in the San Marcos River.  To drain the water from around Thompson’s Island by removing Capes Dam would also drain water from Glover’s Island at Rio Vista, which accounts for another 1/6 of the clean water in the San Marcos River.  We can not afford to dry out  half of our little piece of pristine water in this tiny, precious river.

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 22 February 2016

Without any public input City Council held a workshop with only on presenter despite a gallery full of PhDs. and is now scheduling a vote without any debate.  Please write now to save Thompsons's Islands.

Thompson’s Island has been home to the endangered Texas Wild Rice and Fountain Darters for over 100 years, according to all published research.  As you can see from the chart in this study above, Cape's Dam creates three times the habitat (WUA - Weighted Usable Area) at Thompson's Island at water levels between 15 Cubic Feet per Second (CFS) and 200 CFS, and therefore we must preserve Thompson's Island by repairing Cape's Dam as soon as possible.

Copyright 2013. Save Thompson's Island. All Rights Reserved.

25 October 2014


Texas Parks and Wildlife spent $300,000 to rebuild the left dam at Thompson's Island to preserve habitat in case of drought.

US Fish and Wildlife rebuilt the right dam at Thompson's Island, just over a decade ago, by hand, to preserve habitat in case of drought..

Texas State University rebuilt the dam at Spring Lake to preserve habitat in case of drought.

The City of San Marcos rebuilt Rio Vista to make it safe.

The whole town enjoys this precious, clear water paradise.  Of course, no one could have dreamed that Rio Vista would be transformed so beautifully, but Recreation, Engineering and Planning incorporated the vegetation, and local fossilized limestone, and granite perfectly to make Rio Vista into the most beautifull, safe waterfall in Texas.  The surveys of visitors to the San Marcos River, and Texas Wildrice and Fountain Darters has indicated that the space created by adequate water makes it possible for the endangered species to thrive and increase right along with the people in the river.  In fact the greatest increase in endangered species habitat happened in 2014 when rock structures were built in the river to direct people opposite the endangered species habitats.  Clearly we can replicate this success to create a legacy of protecting our history and habitat of the San Marcos River.  Please ask the City staff to start, by making Thompson's Island's dams safe.