KILLEEN, Texas (AP) – An invasive underwater weed is spreading in a Central Texas lake popular with anglers, tangling boat propellers and threatening the fish.

The weed is hydrilla, an aquatic plant initially imported and sold as an aquarium plant in the 1950s that has become one of the world’s most invasive plants. Fishing guide Bob Maindelle says its presence is at an all-time high in Stillhouse Hollow Lake, about 13 miles southeast of Killeen.

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“So much hydrilla has now grown in Stillhouse that entire coves are now completely inaccessible to boating anglers because the matted vegetation entangles the propellers of both outboard engines and electric trolling motors, thus prohibiting access,” Maindelle wrote recently in the Killeen Daily Herald.

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The plants are spread by uncleaned boats and form thick mats on water surfaces, changing their pH levels, stripping them of oxygen, restricting native plant growth, blocking nutrients for aquatic animals, and hindering irrigation, recreation and water flow, according to the Texas Invasive Species Institute.

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Furthermore, it can damage water quality and foster the growth of toxic blue-green algae. Such algae were linked to the recent sudden deaths of multiple dogs at nearby Belton Lake.