Crassula helmsii establishes dense populations that can decrease biodiversity, displace native flora, increase oxygen levels, cause flooding, obstruct water flow, and reduce recreational value of lakes or ponds. Submerged and floating populations can grow in depth up to 10m and displace macrophytes in depths up 8 m with densities reaching 1 kg dw/m2, emerged populations can reach densities up to 45kg fresh weight/m². It is extremely competitive and significantly reduces the germination of native plants. It can completely suppress native species within few years of its introduction. Such reduction and displacement of native species can result in reduced conservation value of nature reserves. C. helmsii may cause reduction of diatom populations as in the case of Synedta delicatissima in England. It can increase oxygen levels, change pH, and alter light transmission in lakes and ponds which may in turn cause decline in intvertebrates, frogs, newts, and fishes. The increase in biomass in water bodies caused by C. helmsii populations can raise water levels and result in flooding. Dense mats of C. helmsii harm the attractiveness and recreational potential of ponds and lakes by reducing accessibility for angling or boating. Its growth may also clog waterways and drainages (Berwick, 2009; Dawson & Warman, 1987; Dawson 1996, Hussner 2008, Hussner, 2009; Langdon et al, 2004; Linton & Goulder, 2000; Minchin, 2008; SNH, 2009).\r\n
C. helmsii utilizes Crassulacean acid metabolism (CAM) which enables it to take up CO2 during the night and gives it a significant competitive advantage over other macrophytes. This is especially beneficial as aquatic environments generally have limited inorganic carbon (Klavsen &Maberly, 2009; Dawson & Warman, 1987).

Preventative measures: Several measures can be taken to prevent the establishment of Crassula helmsii. Its sale should be restricted in gardens centers, supermarkets, aquarists, and other retailers. Public awareness campaigns should provide information on the environmental and economic impacts of C. helmsii with focus on key groups associated with its import and sale. Removal of domestic plantings in ponds and aquariums and replacement with native species should be encouraged. If established, mesh netting can be used to prevent the spread of C. helmsii to uninvaded bodies of water (Kelly & Maguire, 2009; Berwick, 2009).
Physical removal: Hand pulling of Crassula helmsii is considered to be ineffective as regrowth is very rapid. Mechanical removal of C. helmsii is not recommended because small fragments released into the water column can travel downstream to colonize new sites or recolonize the treated area. Dredging material can be effective for emergent and submerged material as C. helmsii is shallow rooted however it could potentially damage the natural seed bank. Creating shaded areas by covering with black plastic of UV sheeting for up to 6 months has been successful and is very effective when combined with herbicide treatment. Burial with more than 20 cm of soil can result in 100% mortality but is labor intensive and causes much disturbance (Berwick, 2009; CEH, 2004; Bridge, 2005).
Biological control: Grass carp (Ctenopharyngodon idella) feed on C. helmsii, although it is not their preferred food source. A large scale trial confirmed the some control of C. helmsii accompanied by an increase in macrophyte species diversity. However, C. idella are reported to not survive well in waters with a high fluctuations of dissolved oxygen, which is associated with dense C. helmsii populations. Additionally C. idella is also an invasive species that may establish and cause a ecological impacts of its own (Berwick, 2009; Dawson & Warman, 1987). Chrysomelid and curculionid beetles have also been suggested as potential biological controls (Gassman et al, 2006).
Chemical control: Diquat alginate (Midstream) has been found to be the most effective chemical control of C. helmsii with a 95% kill rate and is the only chemical that can effectively kills submerged plants. However, it has been removed from the EU list of acceptable herbicides and has been determined unsafe for aquatic use. Dichlobenil (Casoron G or Midstream GSR) is also recommended but it too will soon be withdrawn from the market. Glyphosate (Roundup biactive) has a 50% kill rate and is the recommended method of treating emergent C. helmsii. Glysophate is most successful when treating before and after mechanical removal or on a new infestation and can be combined with adjuvant TopFilm to increase effectiveness (Berwick, 2009; CEH, 2004; Kelly & Maguire, 2009).The use of Waipuna hot foam, a biodegradable organic compound of coconut and corn sugar which breaks down the cellular structure of the plant, has a 50% kill rate, but primarily kills only the top layers of the plant. Waipuna foam has several advantages over herbicides. It is not weather dependent and can be used in breezy conditions and light rain. Unlike herbicide treatments there is no requirement for special safety equipment. The foam can be applied with accuracy and without damage to adjacent plants. It is also non-toxic to other wildlife (Berwick, 2009; Bridge, 2005).
Integrated management: The combination of methods physical removal, shading, and herbicide treatment has been found to be the most effective means for controlling C helmsii populations. The spraying of plant material with herbicide followed by covering with black or UV sheeting or physical removal are both effective and may be repeated until eradication is obtained (CEH, 2004; Kelly & Maguire, 2009).