Water hyacinth hotspots in the Ugandan waters of Lake Victoria in 1994–2012: implications for management

Abstract

Water hyacinth invaded Lake Victoria in the 1980s and, by 1998, had attained peak coverage of approximately 2 000 ha in the Ugandan waters of the lake. Control interventions, especially via biological means, significantly reduced the weed's coverage to non-nuisance levels (<10 ha) by 1999. Although resurgence was noticed in 2001, total coverage never reached the infestation levels attained between 1994 and 1998. By March 2012, infestations still occurred in hotspot bays, including MacDonald (52.1 ha, SE 3.0), Fielding (38.0 ha, SE 1.4), Bunjako (33.7 ha, SE 1.9), Murchison (17.1 ha, SE 0.9), Lwera (8.5 ha, SE 0.3), Napoleon Gulf (2.9 ha, SE 0.3) and Berkeley (2.1 ha, SE 0.1), in addition to some bays of the Ssesse Islands (47.8 ha, SE 0.5) and on the Kagera River. These hotspots were characterised by shelter from offshore winds and ample macronutrients (NO₃-N > 13.8 µg l⁻¹, SE 1.6; SRP > 17.2 µg l⁻¹, SE 3.2) in the water column. Control efforts, mainly the use of biological control agents on a large scale, manual and mechanical removal at strategic sites, plus a reduction in nutrient loading, should therefore target the identified hotspot bays of the lake.